I always have autonomy on. But I'm a bit OCD so I can't just let my sims uncontrolled. Also as I play challenges I usually have them skilling. But what I like to do for autonomy to manifest is to have "events" where I'll have many sims interacting uncontrolled. Like parties or some community events. This is also one of the reasons I like having businesses. I can control my sim and keep my OCD sanity but at the same time I observe sims from other families interact freely and form relationships.
For example I move a new family in my hood and realize their teen children are ideal matches for other family already in hood. Oh, I had all the couples planned in my head already. But before their turn in rotation I've played my farmer family running Grocery store. These teens were visiting it as well and formed absolutely different relationships from socializing there. One couple I was planning for had a festering grudge ). That's totally fine for me. But had I controlled them first they would end up in couples I've planed for them that's for sure.