Yeah, I ended up doing the same thing last night. Sometimes use it, sometimes don't. Can't really predict the rage spikes well enough to use it reactively--mostly because it doesn't seem to change the existing cooldown of a Heroic Strike.
(e.g. if you realize, 'oh crap I have too much Rage' but you just pressed Heroic Strike, it will still have a 2.5s cooldown after you use Inner Rage anyway. Using Inner Rage should probably reset the cooldown of Heroic Strike... but they were probably concerned about PvP burst with that or something.)
If the only thing an ability serves to do is clutter up our bars or macro list without adding any gameplay, there isn't much reason for it to be in the game.