Pretty much everyone should consider purchasing at some point a black eye shadow so here are some things to keep in mind as you're choosing it.
First off, why should you consider purchasing black? It is a very versatile and useful color to have on hand. You can use it at your crease for your makeup. You can use it over an eyeliner to bolster its blackness. You could also use it over an eyeliner to smudge the line. And one thing that folks often forget about is that you don't need to use all over the crease but you could have just a little bit to darken it. There are many options to use black.
I think that black eye shadow has suffered from a bad rep that it makes you look like a raccoon and, therefore, shouldn't be used. That'd be only true if you do apply it in a raccoon mask sort of way.
Eye shadows come in various finishes (matte, frost, shimmery, sparkly, etc.). Which one you pick will have a different look... and may have a different use.
Matte: A matte black will make the area where you applied it look like it's receding. As such, you may want to use a matte black at the crease or over an eyeliner.
Shimmery: Here, I mean anything that shimmers (so frost, sparkly, whatever). A shimmery black will tend to make the area appear to stand out. If you want to do a smokey eye with a black eye shadow, I'd recommend using a shimmery black, especially if you will do this for stage. Also, if you have a very deep crease, you may want to select a shimmery black to apply at the crease so as not to further deepen the look of the crease.
I actually own a few matte blacks (pressed powder and loose shadow) and several shimmery blacks. The shimmery blacks I own have different looks to them: one has a golden shimmer to it, one has a silver shimmer, one has an iridescent shimmer, etc. It actually often happens that the blacks are part of a palette so they came with but I did choose certain shimmery blacks on purpose.
That being said, if your budget is tight and you can purchase only one black, I'd go with a shimmery finish as it will be the one that will be the most versatile.
Also, if you've ever tried a smokey eye with black and were dissatisfied with the result, try again but with a shimmery black. You'll see that it will help quite a bit.