I considered doing this or buying a house that already had an ADU/casita when we were house shopping, but I have a very different situation with being mostly home alone during the day and a dedicated room in the house for an office. I still think this might be an ideal though, because having a physically separate space has both psychological and physical advantages. Particularly, I wish I could pre-wire a /lot/ of networking in the space and separately air condition it, because I prefer much colder temperatures and it'd be cheaper to keep a separate office at 68F and the house at 74F than try to keep the house at 68-70F.