The berries rarely taste good off the tree. There are exceptions, I think Cerulea has palatable berries and there are numerous cultivars and crosses specifically designed to give a better tasting fresh berry. Elder has some great strengths though which make it such a worthwhile plant to keep. For me, it's two greatest assets are that it makes such a good wine and that the flowers have a superb flavour when used in drinks and preserves. I recently saw the taste of the flowers likened to lychies and I think that's pretty dead on, elderflowers perhaps being even nicer. If you're in any doubt whether to keep it, wait until it's big enough to produce around 5 flower heads and make some elderflower champagne (an easy task). My guess is you'll want to keep it after that. :)

Elderberry jelly is quite good, the flower clusters are attractive from a distance, and few plants could be easier to grow. It also will stand however much trimming you care to give it. It is a host to Pierces Disease so someone trying to grow bunch grapes in zone 8 (or warmer) where that disease is important might consider this.

I once heard of the flower clusters being cooked. Dip them in whipped eggs and then briefly into hot oil in a frying pan.

They are partially self-fertile, but for better fruit production, you need to have another elderberry within 60 feet.

Chances are you have a Common elderberry (Sambucus nigra subsp. canadensis), which is native to the Eastern U.S. and grows as a bush to 6-8 feet. The European elderberry, Sambucus nigra, is more upright/tree-like, but about the same height. These both have dark purple berries. There is also Sambucus nigra subsp. cerulea, which has blue berries and is native to the West -- I've never seen one. There is also a completely different species, Sambucus racemosa, that has posionous red berries (not purple or blue) that are NOT edible, even when cooked.

They can stand lots of pruning, but keep in mind most fruit is born on 2-year canes/shoots. Each shoot will produce well for a couple years, then remove it. Water frequently the first year because the roots are shallow.

Fruit quality depends on cultivar, although even the "ornamental" cultivars produce usable fruit. All need to be cooked due to cyanide content -- the toxicity is low, but eating the raw fruit can cause nausea. Elderberry wine is very popular here.

The common elderberry I have growing like weeds at my place has red berries. Birds love them but they are somewhat poisonous to humans so don't use them. Which is too bad cause they are all over the place

I'd dig it out, asap.
It's really invasive and the things you can make with it don't outweigh the hassle of trying to control it IMO.

It is native across much of the United States. It a good plant to have if you have the room move it along an edge somewhere. It is very showy for a week or so late spring and I like the look of the dark berries for landscape purposes. It does make a good wine, but its a pain the butt to make. I planted 50 of them last year,, mostly for wildlife purposes, it is a preferred browse of the whitetail deer in my area.