I'm a 'warning first' advocate, it's one of the spirit-of-the-game things I was taught as a kid. Similarly, I walk if I know I've nicked it, I let an oppo bowler know if he's close to no-balling and I've even halted an oppo bowler from running in if his captain has accidentally positioned 3 behind square. I just think there is honour in our game that transcends the winning, and that's something i feel is worth preserving.
But then, I just play Sunday 2s cricket, so it's not life or death!