[sneaK]

Just an added bit of info, I believe that this extension still fixes certain server crash exploits, regardless of sv_clamp_unsafe_velocities value. I've had several users attempting to crash a few of my servers recently, interestingly enough one of them is a competitive server, where sv_clamp_unsafe_velocities is of course set to 1.

tl;dr It's not just for surf servers, I believe every server should be running this. Exploiters be going wild.