Unless the leaves are so thick and matted that they're impeding water (and therefore air) movement into the soil then it's just fine.

Most all of the time it's just fine, especially during cooler parts of the year where less water movement and less biological activity in the soil is taking place. It's generally only an issue when it piles up thickly and for one reason of another gets matted into a semi-rigid sheet.

What nc-crn said. If it's not a nasty, wet, matted-down mess, It's all good as far as I'm concerned.

Leaves are a mulch. The only problem with leaving those tree leaves on planting beds is that most of us have been so conditioned to think they are "bad" that people go to great lengths to get rid of a valuable resource.
Tree and shrub leaves are a good source of plant nutrients, however whole tree leaves can suppress plant growth if piled on too thickly, although some plants will simply try to push them out of the way.

Here is a link that might be useful: Nutrients in tree leaves

Leaves can be used as much to prevent weeds, keep moisture..
But if you want them to be composted you need to mix and till into the soil. This way the microbes and worms can get into them. Left on the surface( under trees, shrubs) they will eventually break down and turn into topsoil. That is how it happens in the wild nature. When we put them in our compost pile, we are just accelerating the process.

I like raking all the leaves on my property, shredding them and put them on my beds. Since that quantity is never enough, I grab the leaves my neighbors put out to the curb and shred them too to add to the beds. I then top dress the beds with pinestraw.

What did Mother Nature do with all those horrible leaves before people came along? Oh that's right, She left them on the ground to return to the soil. :-]

That's my whimsical response. The serious one is, if you're in an area where it's now winter, just let them be. They will help smooth out freeze/thaw cycles which is what mulch is supposed to do. In spring, remove whatever you need to so your delicate plants (bulbs, etc.) that are sprouting can get to the light. Put those into the compost. If that's not a concern, you could pretty much leave them right there, add a little mulch over them and let them become part of the garden.

I purposely gather leaves at the leaf dump to put under my wood mulch to make the mulch last longer and for my shade plants. My trees are too small for me to just gather from them and put where needed. I have lots of trees to mulch. I also gather some to add to greens in compost.

I have never removed leaves from my beds except those around the stems of the more delicate plants, but I still leave them in the beds to be covered over with more mulch in the Spring. I never have enough fall leaves and always wish I had gathered more when Springtime rolls around.

I wish we had Pine straw for sale here in Pa. I gather some from the leaf dump in fall, but there are never enough. I like the leaves with pine straw on top for beds. I just wish I could access more pine needles/straw. We have to rake from under trees, or go to the fall leaf dump and gather from folks who rake theirs and bring it to the compost site/leaf dump. The pine straw bales for sale market is a southern thing unfortunately.

Shredded leaves as mulch, shredded leaves over previous mulch, leaves in compost, leaves bagged & ready for...more compost. Leaves are a gift from the mother, never waste them. Earthworms love leaves, soils loves earthworms, plants will love the soil.
I have no leaf source in my yard, mine all come from parks.

I use the leaves as mulch, and don't buy any bags. When I noticed a guy clearing the leaves out of beds around the bank across the street, I asked him to dump some on my beds, which he was more than happy to do. Our trees don't drop enough to do the job because, as said, they disappear quickly. When DH got home, he grabbed a couple loads to put in our dog house. (We tried putting a blanket in there, a mattress, but the dumb dog ate them.)

OK. I have to add one more point.

Most people keep their perennial/flower beds neat and orderly. That is why, packing fall leaves is not pretty. So you blow those leaves away and mulch it in an orderly fashion that looks nice. Isn't that why we plant flowers in the first place ?!

My beds are planted along paths. I strive to mimic what I have seen in nature out on hikes & some plants are native while others are cultivars of natives. Leaf mold mixed with shredded leaves makes outstanding mulch & looks neat but not necessary tidy. It lends a natural look. In any case no leaf is wasted if I can help it. I also find using leaves in the garden makes my yard the bird hot spot. They comb through the plants & pick off pests & kick the mulch around as they forage. They need all the help they can get in this day & age so I'm happy they accept what I have inadverantly offered. & anyway, everything justs melts into the ground in a few months.

Perception is everything. If someone sold shredded leaves as mulch in cute plastic bags many people would spend money purchasing that while spending money raking, bagging, and getting rid of the leaves that fell on their gardens and yard.
Whole leaves should not be left on a flower garden with perennials growing, but shredded leaves look much like wood chips and can be used.

I would say never till leaves into the soil, let the earthworms do it. Leaves do not break down well in soil or in compost piles. Composting is primarily a bacterial breakdown. Leaves fall and layer in the forest, become nearly anaerobic and are broken down by fungi...hence leaf mold. After three years of formation leaf mold becomes a superior soil ingredient.