I tend to shelf a servant for the most part if they’re bond 10. Typically there are others that can do the job and it forces me to get used to using a different servant.
There are exceptions of course, for instance in Setsubun where servants had a cooldown for you to use them again, so it was nice bringing out my bond 10 servants again even if that event is rough as far as the sheer amount of time it takes to complete even if the difficulty is low.
As for other exceptions:
- FSN Cu sometimes gets tossed on the back when I’m not sure if the others can fully complete the job, but that’s not very often since in those cases I ended up not needing to bring him.
- I think I brought Proto Cu off the bench once or twice for a difficult Wild Beast battle.
- Herc I think a brought off the bench for a boss or two, not sure.
- Emiya, Carmilla, Cu Caster and Angra have stayed on the bench, though I know a few times I was tempted to bring Carmilla off the bench for more anti-female damage.
Though when certain really useful units reach bond 10 (such as Waver, Drake, Altera and Arash) it’ll be more difficult to avoid taking them off the bench, but that’s why I’m glad the bond grails are coming up.
More recently I’ve adjusted my bond farming backline to characters whose bond CEs I’d like to try out but I’m not likely to use that servant much (like Kiyohime) since if I farm up someone’s bond who would already get plenty of bond from general use then they’ll hit the cap and get shelved without me using them much, which wouldn’t be good (this happened with Herc).