The basic idea is that in a tourney, you don't get money for winning chips, like you do in a cash game. You get chips for finishing in a higher position. 3 people calling the short stack make it pretty likely he's going home and you all increase your EV. If you bet everybody out and the SS quadrupled up through you, you have at best kept your EV about the same and may have decreased it depending on the former SS's position relative to you.
My thoughts on that are bet if you think you have everyone beat. If they can't draw out on you, size your bet so they have to call. If you know you have the SS beat but can be drawn out on, don't give them odds
to call. I tend to assume people get this idea, and make note of those who don't at the table. I count it as predictive of other bad plays.
Long story short, knocking the short stack out is always +EV. Raising sometimes is if you really have a hand.