Say you're testing a new offer on about $20 a day in one ad set. Advantage+ placements looks like the obvious default, since Meta can push spend toward whatever is converting. But at that budget the algorithm can dump almost everything into Reels or Stories, and then you never find out whether Feed would have done better for that offer.
I'd start with manual placements for the first couple of weeks, Feed plus Reels, and only open it up once you can see which placement actually gets cheap results. You give up a little efficiency early, but you get a test you can actually read. Has anyone seen Advantage+ placements clearly help under roughly $50 a day, or does it mostly hide the answer?