Think they covered it OP. UC is about maximizing damage during time frames. example time frames are on initial pull when you have aggressive DPS, times when the group is having issues on DPS checks, during burn phases, etc. The extra damage also means extra threat. but you usually want to avoid using things that ignore the damage penalty as well, like inner beast, and you want to make sure you maximize it by staying in Defiance until it's out (as an example if you want to build threat before switching to Deliverance).

It's more of a timed skill then a spam as much as available. IB tends to be the default go-to (for obvious reasons), UC during burn phases or off the gate for max DPS/threat. stuff like that. I use it allot when im running with max geared DPS. fighting a Dragoon for threat isn't a fun thing usually if you pop UC out of the gate it helps allot.