stealing the blinds

Like so many things in poker depends on more then one factor. In the early stage of a tournament where everyone has 75-100x the BB it's completely pointless. Later when the average stack has 5-10 times the BB it's necessary to survive.

The trick is to observe players. If you've seen a guy call a shortstack all-in with just queen high then you want to be careful with him. Same way you don't push all-in with 4BB's if the chip leader is waiting to act with 40 BB's.