It really depends on the legacy challenge I'm playing. I'm doing Not So Berry and I make my Sims change houses per generation (maybe move multiple times depending on generation rules).
But I did the original legacy challenge too w/scoring where you're supposed to stay in the same house the entire 10 generations. I built my own house and I think I stayed in it for 5 or 6 generations and then decided to move for the remainder of the challenge.
I'm one of those players that gets bored pretty easily. So unless I have some attachment to a house, I typically like to move per generation.