Playing fallout shelter on my iPad-
Things started to really break down at around 30 colonists. iPad just couldn't keep up. Everything took longer to do, base needs were right at the limit of having to expand, yadda yadda.
Come back after sleeping, all hell breaks loose. Population explosion from all the babies, radio seekers & returning wastelanders. The wastelanders I didn't recall died of course, so I've got about 6 corpses to revive. Everything's depleted. I'm overflowing with weaponry & equipment I need to disperse & sell.
Nasty streak of rush failures puts everything into a red slump. No one's happy/healthy as I try to process the wastelanders/equipment, build new buildings EVERYWHERE to meet the demand, try to look at the new colonists and assign their roles, manage the disasters, (as ALWAYS there was a team of Raiders chomping at the bit for my return, itching to further complicate things), and by now, at ~48 colonists, I just CAN'Tdeal with the choking UI anymore. Everything takes 3-10x as long as it should, and I can't keep up.
I think vault 278 is at the end of the line.
In other news, I think the primary purpose of level is to make sure dwellers 'die' eventually. They become too expensive to revive.
Also, 3 tiles is the max room size.