In most of my "non-simlit" saves that I play a lot, I am only playing one household. But I have a lot of saves. I think currently I have about 16 saves that I play just for fun which are all one household only. I play whichever one I feel like playing in any given session. Even in the few other saves where I do play more than one household, I typically have a "main" household that gets most of the time and attention, and I only play the others for short and infrequent stints.
I think there are a couple reasons why I like sticking with one household. The main one is that I just get emotionally involved in what those specific sims are doing, and become very attached to them. I don't really want to play other households in that save, because then I wouldn't be playing with the main one. I don't like seeing my main sims walking around in public places doing things that don't fit their story when I am not able to control them.
I play with aging turned off because I'm not really interested in generational play. What appeals to me about sticking with one set of sims for a very long time is being able to create very complex stories for them in my head (regardless of whether I write the stories down or not). Spending so much time with them makes them really come alive for me as characters and people. There is plenty of time for subtle details, backstory, subplots, random adventure arcs, complex relationships, and character growth.
I take a TON of screenshots. Sometimes upwards of 100 screenshots during a single play session. I save them in separate folders for each save. I give them captions so I know what was going on story-wise in my head when I took them. Those screenshots help me think about the story as I am playing. And if I go away for a long time, I can use the screenshots to remind me what was happening in the story when I come back.
I will say that right now my playstyle is hindered by the bug that makes sims keep moving when the game is paused. That makes it hard for me to capture precise moments in the story with screenshots. So, lately, I have been not playing with a lot of my main household saves very much. I've been focusing on my more heavily staged simlit saves and my more superficial "messing around" play saves instead. Hopefully this will get fixed though.