The exception to the "lighter is better" rule is sailplanes or gliders. They often intentionally carry ballast to increase the weight of the plane for better penetration into headwinds. Full scale sailplanes often have water ballast tanks. The water can be dumped in flight so the plane can land light.

I once rode in an almost empty Boeing 737 for a short hop from Tampa to Jacksonville FLA, meaning that they probably had a light fuel load as well. It must have been off the ground after only a quarter mile or so. What a contrast to the same plane full of passengers and with full fuel tanks!