The thing is, I do exactly what you mean by "stacking up" activities so my sim is never standing around, but I do give them a super long leash (lol makes it sound super technical) to work with. That way, things get interesting and you learn more about who your sim really is by letting them pursue their hidden passions on their own. For example, I would never have known my Sim liked this other sim if I hadn't walked off and come back to my computer seeing her flirting with him. You also get to learn some of their characteristic interests. It was funny to see how one of my sims was obsessed with practicing the guitar, a skill I don't think I would have chosen for her to work on normally ?. Of course, some occasions call for less autonomy, like when you want to get a group picture at a special wedding or when you have a certain romantic interest saved for your sim and you don't want it ruined by random flirting ?