I've actually done this a couple of times.
Once, because my brother was the absolute underdog in a match (I hadn't been playing with him). The other guys were either camping noobs or the cornucopia-seize 'ers. I helped him out, and he still ended up dying (not much of a chance).
The second time was a couple days ago when I got into the same server as him. He and his teammate, who he was going to let win, were on the other side of the map from the last guy alive. And whaddaya know? That noob had no armor and wooden sword. He was sitting in a tree, and there were 30 more minutes left in the game; so, yes, I did tell him where the noob was, and yes, it did speed up the game by 30 minutes. People were actually happy, because it was obvious he was going to lose.