If you guys havn't listened to it, Keits and Skisonic have a really good discussion about it in the latest ep of Wakeup SRK which gives some good insight and some pros and cons about situations.
I basicly agree with the notion that you don't wanna be the first one to throw it out. Against LVL 3 sent whores (Such as myself -_-) you can use it to negate the chip damage which is really usefull, and if somone uses it to kill one of your characters, you can bust it out to make the match level again.
In the end it's really situational as to when to use it, the best time to use is it when it won't goto waste
