[argyleaf]

I can't speak to endurance (I got into IF after my endurance-athlete days) but I know that body weight-based athletes do this to perform better. My experience is specific to rock climbing.

When you are right at the edge of your abilities being just a couple pounds lighter can feel like a world of difference (people hone down their rack to precisely what they need for a route, nothing more), especially on sport and boulder problems. My anecdata points to it being great for the project/performative aspects of the sport but as a tool for consistent progression/improvement, I am less confident in stating anything.