Liquid levels at minimum sufficient?

Hello guys, I was thinking today about whether it would be enough for liquids in the car if they were always only standing/replenished to a minimum? I don’t know how sensible this idea is, but after all, you would save a few kilos of weight in motorsports or earn more/less. Why should it be located in the middle between min and max or why not always fill up to max (oil, cooling fluid etc.)?