If they fall off at a light touch or shake they've done their job. If you can live with the sight of them don't pull them off if still attached.

You need to find out why so many leaves are turning yellow. Did you move it recently? Ficus benjamina does not like to be moved, even from one spot in your home to another and will lose a lot of leaves, but it will recover if not moved for awhile.

Can I shake the plant so that the leaves fall or remove them manually when it is enough to touch them to make them fall? I remember (maybe I'm wrong?) reading that ...... it's best not to do this because the plant absorbs microelements from the yellow leaves until they fall. A reduction in the flow of auxin across the abscission zone where the leaf is attached to the branch is the primary driver of the shedding process. A certain level of auxin flow is essential to keep an abscission layer from forming at the leaf attachment point. Anything that reduces the flow of auxin through the abscission zone brings with it the potential for shedding of foliage. Chill (especially sudden), a decrease in light intensity/duration, soil solution issues (too much or too little), nutritional deficiencies, root congestion, poor root health or disease, insect herbivory and diseases, are all cultural influences that can work individually or collectively to slow the flow rate of auxin and cause an abscission layer to form.

The abscission layer is a corky layer that eventually forms a wall between a leaf and the living plant. Once it has formed, no water or nutrients can make way into the plant, and no photosynthate (food/sugar) can be moved from an affected leaf to other plant organs; so, the commonly held idea that dead leaves of branches can somehow rob living parts of the tree of resources like water, nutrients, or photosynthate is not valid. The only benefits that can be ascribed to early removal of dead/dying branches/leaves would come in the form of greater light penetration and air movement to the within the confines of the plant's outline (closer to the trunk).

There is no problem in shaking the tree or gently tugging on a leaf to see if it is ready to be shed. Leaves that don't fall as a result of a jostle or gentle tug, but are obviously dead, should be removed by cutting through the leaf petiole with a pair of scissors so there is no risk of damage to the area in leaf axils where dormant/latent buds are waiting to be activated. This would be immediately distal to (above) where the leaf is attached.

Ficus benjamina does not like to be moved, even from one spot in your home to another and will lose a lot of leaves. This paints with a brush too broad. Generally speaking, leaf loss resulting from repositioning a tree only occurs when the tree is moved to a spot with appreciably lower light, which reduces the flow of auxin across the abscission zone. Moving a tree to brighter light doesn't often cause shedding of foliage UNLESS to leaf itself is incapable of adapting to the increase in light. Something I wrote about the topic:

Light Acclimatization

The degree to which a leaf can 'acclimate' to changes in photo load is limited. IOW, you can't expect a leaf that emerged under a full sun light load to acclimate to light levels in a dim corner, any more than you can expect a leaf that emerged in a dim corner to acclimate to a full sun site; this, no matter how long you allow for gradual acclimation. Too, the plant's ability to adapt to higher light loads is greater than its ability to adapt to lesser light loads.

Using a 1-10 numerical example to illustrate (numerical value of 1 is low light, 10 is high light): If a leaf emerges where the light level is measured at 5 units, it's range of adjustment might only be to 3.5 on the low side, but 8 to 8.5 on the high side. When the level of adjustment required is greater than what the plant is genetically programmed to deal with, the leaf is shed, and this can occur with conspicuous or relatively inconspicuous damage to the leaf. While shed leaves can never be replaced, per se, new branches can form (with new leaves along the new branches) in the axils of dying leaves or from latent buds immediately above scars left by shed leaves. Too, whenever a new leaf appears it will be perfectly acclimated to whatever the photo load is where the plant is positioned (within the limits of what it is genetically programmed to tolerate).

Al

You need to find out why so many leaves are turning yellow. Did you move it recently? Ficus benjamina does not like to be moved, even from one spot in your home to another and will lose a lot of leaves, but it will recover if not moved for awhile.

As @tapla (mid-Michigan, USDA z5b-6a) explained, the leaves fall due to the to the lowering of temperatures and the reduction of the hours of light (obviously since the ficuses have not been pruned and there is also congestion of the roots, the phenomenon occurs to a greater extent). Here in Naples, Italy, the minimum temperatures in winter never drop below zero degrees centigrade and the maximum temperatures rarely fall below 10 degrees: for this reason I leave the ficuses on the terrace. I think that if I moved the plants inside the house (in reality I wouldn't have space) they would suffer less from the cold, but more from the less light and therefore little would change. The situation would be different if the temperatures were lower. Do you agree with me?

The abscission layer is a corky layer that eventually forms a wall between a leaf and the living plant. Once it has formed, no water or nutrients can make way into the plant, and no photosynthate (food/sugar) can be moved from an affected leaf to other plant organs; so, the commonly held idea that dead leaves of branches can somehow rob living parts of the tree of resources like water, nutrients, or photosynthate is not valid. The only benefits that can be ascribed to early removal of dead/dying branches/leaves would come in the form of greater light penetration and air movement to the within the confines of the plant's outline (closer to the trunk).

Al, do you know why I was convinced that you claimed that the plant uses what is contained in the leaves that are yellowing? Because in other discussions you wrote that the plant robs mobile nutrients from older foliage to use as the building blocks for new foliage, then sheds the older foliage. Therefore, I imagined that the plant continues to rob mobile nutrients from the old leaves until they fall off spontaneously.

You're referring to: "The first phase of leaf abscission (shedding) is resorption, during which the plant extracts and repurposes nutrients which are mobile in the plant (nitrogen, phosphorous, potassium, magnesium) and other biocompounds." You'll notice that when magnesium is reclaimed from leaves it causes breakdown of the green pigment chlorophyll; this, because magnesium is central to the chlorophyll molecule. When chlorophyll molecules are broken down, chlorophyll can no longer mask colors provided by the other pigments, so the yellows, reds, and oranges, of the carotenoids become expressive.

Once the abscission layer has formed, exchange of nutrients and other biocompounds across the abscission zone is no longer possible. IOW, all resorption occurs before the abscission layer is complete. Once complete, the leaves provide no advantage to the plant and can be removed. Trees vary significantly in how tenaciously the leaves remain connected to the plant. My neighbor has a very tall Fagus sylvatica 'Fastigiata' (pyramidal/ columnar beech) which still holds onto all of it's 2023 foliage. If the leaves were to be plucked from this particular tree, there would be significant probability that some latent buds would be damaged. Species in the genus Carpinus (hornbeam) are another plant that, though entirely deciduous, often hold their leaves until the spring push is underway. So, for these species, I do all leaf removal with a pair of defoliating shears.

Al