Activation in more detail than the first post:
Basic stat reminder - 1 frame startup, +2 frame advantage (can move 2 frames before opponent on activation).
Pressure - Bang install activation can be used in the middle of, or even as a way to reset pressure, similar to how TK D nails do. Just be aware that you do 0.5 guard libra damage (but gain more mixup potential, and it's still quite possible to guard break).
Combos - Just landed a move to setup into one of the many awesome FRKZ combos (aka anything?) Activate on your normal hit, and finish the combo like only FRKZ can! In addition, it also used right before Daifunka is used to get more damage out of it, always worth if it will finish it! FRKZ can also be used as sort of a hitconfirm on things such as 5C, daifunka, which normally can't be.
Defense/scouting - FRKZ can help you option select your defenses on wakeup with 6D's frame 1 autoguard (into damaging combos should you connect) or using the invincibility on Daifunka.
There's probably more too somewhere.