[MD_]

One thing not often considered (but that is given a brief mention in TPFAP) is that it is sometimes in your best interests to save the all-in player when it doesn't cost anything to do so. This could be the case on the bubble where you have a big stack and are picking up lots of blinds. In this case trying to prevent an opponent from beating the all-in guy by betting with nothing can be strategically sound. Of course accidentally winning the hand yourself is often good too, but the main point is to prevent a live opponent from winning.

-MD