This "opens up" the eyes a bit, so you do not get it there the skull feeling that the eyes are two black holes. It will be a little easier to carry up the sweeping then :)
Before I start applying the black eye shadow, I protect the basic make-up under the eyes with a thick layer loose powder.
I only do this on make-up with dark shadows, if eye shadow falls under the eye then it does nothing - it is easily polished off with the loose powder when you are done!
A black sweeper works at any party and fits all outfits!
You can also easily vary a black sweep to what you feel best in, for example skip the dark eye shadow on the lower lash line for a less intense impression.