I think no one really knows yet. My understanding is that boosters increase antibodies, which prevents illness from ever happening. Those wane over time, but your body still has immune memory should you get infected. When that occurs, it still takes a while (3-5 days) for your body to remember how to make the antibodies. You can still get sick, but your body will know how to fight it and prevent the serious hospitalizations. If you're somebody who can't ever even get sick, boosters are probably the correct course of action. But if you don't have any co-morbidities, you should be okay with the normal dosage. Of course, time will tell on that. I got a lot of that from the following Atlantic article, and it was retweeted from a lot of vaccine equity docs and scientists, so there's likely some of that slant to it. https://www.theatlantic.com/ideas/archive/2021/08/americans-are-losing-sight-endgame/619916/