i see no difference in either.
either you leave a game you have no chance of winning or you choose not to join a game you have no chance of winning.
in the end you already counted the loss.
unless you wait till you get kicked then you are holding a spot away from someone who might not give a crap about winning and just wants to play.
if you find yourself doing this then you are just another statwhore who cares about the W/L and K/D.
personally i rather waste my times in competitive matches then stick around on the losing end of a blow out.
i play modes like DOM and HQ and i play the objective hard as my stats suggest and if im on a team not willing to do that i leave.
i also refuse to join a game where dogs and swarm are already up and running but i always count that loss by not sitting around and wait for the kick,
the only stats i care about are captures and defends.