One thing you usually can't do, though, is rearrange walls. While very much a proponent of renting vs. buying (I'm in Germany), sometimes the layout of flats is atrocious. We have a tiny kitchen with barely enough space for a single person to work in, a gigantic living room with mostly windows and no walls to put shelves against, and despite it being 90 m² it's only three rooms which will likely prove problematic once we have kids above a certain age.

Sometimes I wonder how such layouts are created. Presumably by people who don't have to live there. Or live a very different life (eating out vs. cooking, maybe). That's one thing you can do better when building a house, although when buying one you could probably change it at great expenses as well.