My parents have one that came with the house.
It's about 10x5 and it helps make a really nice outlook from the house (patio and flower beds around it then the big grass garden with trees beyond). We always joke every swim costs £500 and in all honestly we're probably not far off - they heat it with a heat exchanger, chemicals are expensive and there's all the kit (a 'hoover' thing you set on, solar cover etc) and the pump that always has something going wrong, it's been resurfaced, new mosaic edge, new lights... you name it, it won't last forever in a pool. It requires extremely regular monitoring, cleaning and chemicals - if you leave it a couple of weeks you will not be able to use it for a few days while you get the balance back.
They don't go in it much and there'll be weeks going by when we say 'we must make use of the pool' and just don't, and are really wasteful of it.
But, we had it growing up as kids and used it a lot then, and now my parents have 4 grandkids, so when they come and use it, it's genuinely brilliant. They've all learnt to swim in 'Nanny's pool' which has been really special, and lots of amazing memories, and we've all loved the privacy and ease of just behaving however you like that a private pool has. I haven't been to a public pool in about 20 years now - the noises and smell and other people... your own private one is another world.
For at least 10 years my parents decide at the end of each season 'we'll fill it in' but the youngest kid is 4 so we keep on giving in 'another year'. So - something's keeping them decide to keep the pool going....
But - it eats a LOT of money so you need to be happy with that.