What are the benefits of using Perforce instead of Subversion?

Perforce licensing slides down in cost as number of seats goes up, as I recall. So it's not exactly $900 per seat. It's also a server-based license; you pay for total number of human developers using it, not per machine client using it. So, if you're a shop of 200 people, the 200 seat license lets them all use perforce, even from home.