Cymbal Used

"Fast" usually is a term that simply refers to thinner cymbals with shorter decay. For example, Paiste offers (from thinnest to thickest):

Paiste Signature Fast Crash
Paiste Signature Full Crash
Paiste Signature Power Crash

They're made from the same alloy and hammering techniques, just with different weights.

If you have a lot of cymbals in your setup, a fast crash would be a good way to go, since it gets out of your way fast (hence the name). However, I find splashes will also do well in this department.

The potential downsides may be that thinner crashes have less "ping", as in you can't really ride on it as well as a thicker cymbal. It all depends on what you're looking for, however.