Well, most of the time fury seems to be a waste of pillz...
It can be quite useful in many situations:
You have a character with +X life per damage. Using fury means doing at least 4 damages and sometime even more (Kenny with +2 lifes per damage mean you'll get 6 more damages!).
If you apply lesson #2 "thinking in less than 4 rounds", fury is a good and quite unexpected way to reach your KO
Dont use fury at all if you really needs to win most of the forthcoming rounds. You better save thoses 3 pillz to get an attack advantage.
One more thing.If you are using Shann,Conrvus,Anton and such characters who recharge your pills it is smart to use furry.
But,in some situations it is not so smart to use furry if your opponents power is higher than yours.