Each case is different. A friend of mine had her mother living with her in an annexe which was built for her MiL, who hardly lived to use it. But the friend's mother was very placid and compliant, and moreover would hardly ever leave her bed, so there was no wandering, or being up and down half the night, or fiddling with things, and no incessant questions. She was very content with the TV on all day and my friend managed pretty well with carers coming in a couple of times a day. But it still meant that she and her husband could very rarely go out together, let alone away. Yes, they could have had sitters, but money was already very tight.
And shortly after the mother died, and they could look forward to more of a life together again, he was diagnosed with prostate cancer. Life can be so very cruel.
After the experience of having my FIL to live with us, I knew I could never do it again. I was very fond of FIL, but having always been very stubborn he became a lot more so. He was up and down half the night, banging and shouting and trying to get out at 2 am (and we still had children at school who needed their sleep, never mind me and OH). Among other things he started flying into truly terrifying rages over the most minute things - they were so bad I would have to leave the house and take the dog with me.
We began to look for a suitable care home, and I can't say I ever really felt bad about it. He was already well into his 80s and had had a pretty good life, and we went to a great deal of trouble to find the right care home, where he settled very well.
After this experience, when the time came with my mother, I knew there as no question of doing it again. She did not have the rages, but I knew she could never have been left, even for half an hour, and there would never have been any peace during evenings or weekends, or undisturbd nights for my OH, still working long hours in a demanding job. He was always extremely good with her, but I was not going to expect that of him. And I knew my mother's former self would never have wanted me to. Her own mother had had a degree of dementia during her last few years, and would stay with my mother for a few days at a time. Even that nearly drove her mad, so I know she would have understood.
I supported her at home as best I could, including masses of 'sleepovers' for several years, but when we began to know that she was no longer safe to be left at all, it was time for a care home. But we were extremely lucky in that both parents were self funded, so that we did not have to rely on social services deciding when the time was right. I know there are always a lot of complaints about the 'unfairness' of having to self fund when others get care paid for, but to me, on both occasions it has seemed like a great luxury which we have been very thankful for, to be able to decide when and where.
Might add that if I ever get dementia, God forbid, I would NEVER want either of my daughters to put their lives or jobs on hold to care for me. I have expressly told them
that they are never even to think of it.