I don't know, I'm glad I did. It forces you to try new guns, or re-try old ones. Like now I know that I'm an animal with the MG4 grip + RDS, and the RPD is clearly my favorite gun in the game. I used it all the time in the first MW but never went back to it for some reason.

I gave up a LOT of shit on my last prestige though, stuff I don't see myself earning again.

M1014 extended mags (makes it my favorite secondary in the game)
TMP extended mags (plus akimbo, this was deadly and I have still never been killed by it)
Sitrep Pro (CMON who else has bothered with this? I can't be the only one. It's really good if you have a good sound system)
Fall camo on the UMP45
blue tiger on the Mini-UZI (akimbo mini-uzis + akimbo TMPs + steady aim + stopping power = massive LULZ)

All told, you do level up faster, and I felt it getting a little stale when I wasn't gaining levels. It's fucking stupid, it's such a carrot-on-a-stick piece of contrived "replay value" but dammit, I need to level up.