I just bought the lot next door for some of my sims, with the idea of splitting up the family. But it seems as if the sims still treat the original house as their home. That is where they keep coming back to sleep. Is there a way to make this work? Or do you use a second lot for other reasons?

You actually moved them out of the household to there and they still come back? How odd! I split some members off my legacy family to houses across the street 2 times that I can recall, and they stayed living in the other houses. They would come and visit I think and my Sims would visit them, but all knew which place was their current home.

No, I wanted to split the family up. But could not find the option for that. So instead I just sent some of them there, in the hope they would return there after work. But they returned to the original home instead.

I also wonder what other players use a second home for. I mean, I can see the use as a dedicated party place or beach house in same neighbourhood, but I am hoping for some more interesting usecases.

You could use the 2nd house as a studio or workshop. Then, you don't have to clutter up the main house with crafting items. (The glass blowing station from the store is quite massive, for example.)

That is a very good idea.

As for splitting, I actually split people off from my main household. I now recall one other time where I split off one of 2 daugthers and saw later that she had paired off with a vampire and had a few kids!

I understand what you mean. You want them to live on different lots while still being able to control all of them (without switching the active household). I don't know how to do that, I have wanted to do this for long. It would be good to have an option that sets x sims in the household to treat another lot as their home. So you don't have to worry about them doing weird things upon moving them out since you could keep an eye on them. Even with story progression off they still do things you don't wanna.

I remember seeing Not Malcolm have that setup in one of his super rich legacy families. They owned some residential houses.

One of the husbands lived in the "town house" of the family. And I think one of the family members also lived in a house that the family owned but wasn't the main mansion. Maybe it's worth asking how?

You can still have part of your household live in your second house, you just can't use the portrait panel's "go home" option. If you have your sims queued to "go here" to their second house after work, they'll go there. You can also have them shower there, cook there, and sleep there, etc. Though, if you direct a teen to sleep alone at a second property, they'll get spam fines from the police-- think it has something to do with evading curfew even though they technically aren't

In one of my save games I use two lots. My sims are horse people, so I put the horses on a 64 x 64 lot that has a barn and stables on it, while my sims have a regular home that is right next door (the primary home). I've had a lot of issues with it. Idk if it's because of the horses or because they are not on their "home lot". It can be done but for me it's honestly a lot to keep up with lol.

Yeah, I have similar issues when trying to split the household in two. So I ended up creating a workshop like suggested for the second house. It looks like a science lab where my self employed inventor goes to work. This really makes me miss OFB from Sims 2. That would be perfect for a second house.