Hardcore Team Deathmatch.
Why I use 2nd Chance Pro. 4 extra kills, instead of waiting for a respawn.
I play with a tight team, and I know if I'm downed and one of my teammates is nearby they'll raise me, and vice-versa.
If they can't get to me, but see me, they'll put a bullet in my head (either way, robbing the opposing team of a kill.)
I love playing against people who are dead set against this perk, and in the aftergame lobby hearing them curse & rage about it's use when they lose.
http://www.youtube.com/v/CFdJyGPfH1k?fs=1&hl=en_US&hd=1