Which boss needs boon strip?
The only boss, which physically requires boonstrip to be even able to finish, is Vale Guardian. During the 66% and 33% phase of the fight, the blue split has a buff, which makes him take no damage and has to be stripped in order to progress the fight.
Other than that, the only thing that comes to my mind is Xera. If your shard clearers are slow (or just plain bad), you’ll be forced to move her to a new tanking spot through the shard AoEs, which makes her receive a lot of nasty buffs like quickness and fury. In that case, she will probably kill the tank and anyone in her way. Same applies to the ad mobs AFAIK. These boons can be stripped, but you can deal with it in a lot of other ways – wait it out, have a minstrel tank or… (this is probably the best solution) tell your shard clearers to git gud.
I can’t think of any other place in raids, where boonstrip would be required or even beneficial.
For Xera it also depends on your tanking strategy. Pending your groups DPS, there are two tanking methods that keep Xera near the bloodstone shards for an extended period of time. After you kill the shards boon strip becomes relevant for a short period of time.
On deimos, if you don’t break the first saul he steals you boons. This can obviously be prevented by good mechanics, but if you screw up having boon strip is useful.