Useful stuff that can be done with inverted samples

[Saga Musix]

Interesting idea, though of course it's still quite limited (only one cutoff level, no resonance, etc).

[DataCollision]

You can also use an inverted sample alongside a non-inverted sample to remove the vocal track in most instances. It might kill the bass too, but it can be useful for remixes!

[Saga Musix]

The technique you describe only works in some songs, and only due to the fact that vocals are most often mixed dead-centre, just like the bass and maybe drum tracks. It also won't remove reverbs / echos from the vocals.