I add just 3-4 years to my sims' age every RL year, so it's going rather slowly. I still have a few of the YA sims I created back in 2014, now they are pushing their final days, though. So, I guess it's safe to say I ply only one generation. When I add a new world I will create new families and backstories, and some will connect with my existing a few generations back. I normally don't play the past generations though, but i spend some time on developing their characters and implementing them with my rigid system with details affecting them and what they pass on. I guess that's half the fun for me - when creating a new family, by starting a couple generations back they get created by whatever DNA is passed on. I rarely adjust their looks, not even the eyebrows. While doing the trees, I also secure a few family photos for the home(s) of my current time. I know I could just create some photos of random sims and pretend they were relatives, but it would not feel as genuine to me. Nobody else will see this, LOL, maybe I'm focusing a bit too hard on those details :)
Btw: I play with aging off, but every New Years Eve I turn aging back on to let everyone age 1 year. It's slow, but most Winters a handful elders die, and 10-20 babies are born every year, so I get a certain feel of a community rolling along.