I can’t speak for anybody else. But for me?
When I’m working on a delve with a faction team at Level 500, I pump a handful of treasures into the hoard every day. Usually the low-end stuff, but I try and grow the hoard by a level a day, maybe a few levels with the higher-rarity treasures once a week or so. I know it’s not the “optimal” way to do things, nor is it particularly cost effective, but it works for me and feeding a hoard is part of my morning routine.
And I don’t stop growing the hoard until one of two things happens. Either I defeat the delve with the faction team and no longer have a reason to pump stuff into it. Or I reach that subjective point where I make the determination that my failures aren’t a stat-based thing but a “luck” thing – i.e., losing to sky-falling skulls – or a “strategy” thing. And if it’s the latter, I pause adding to the hoard until I determine if my new approach is viable.
My hoard in The Warrens is at 297 because that’s where it was when I finally beat the blasted thing. I had a small number of previous attempts at lower numbers make it to the boss room and two of them even get to a “next skull hit wins” situation before failing, but never regularly enough for me to stop feeding it.
My hoard in City of Thieves is at 295 for the similar reasons. I kept feeding it because it was too necessary (in my opinion) to have raw stats on my side even if I got a room configuration I could work with.
My hoard in Werewoods is at 265, again for similar reasons.
In the delves I’ve completed with a faction team, most of them are in the 150-200 range.