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.
It is an option but it is neither particularly breathable, nor flexible, nor inexpensive.
For some PPE all you are looking for is no-melt (which would leave molten goo on your skin that would increase the damage)or provides a minimal level of protection, e.g. NFPA 70E PPE level 1 for arc flash, suitable to your expected risk exposure.
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.