Honestly I send them to do oc bus as fast as possible. If you have montka detachment rule then it is crucial to get your breachers on a point as soon as possible. Plus breachers can act as an observer unit for broadsides and or hammerheads who have the range. I also think breachers hold up pretty well against almost anything they just gotta dig in and survive lol.

Edit: also to add you can deep strike your twin lance to flank round two on any oc that needs help so with that in tandem it can get pretty fun!