Astronauts on spacewalks famously have to relieve themselves inside their spacesuits. Not only is this uncomfortable for the wearer and unhygienic, it is also wasteful, as—unlike wastewater on board the International Space Station (ISS)—the water in urine from spacewalks is not recycled.
Mass still costs energy to move around. Spacewalks already sound pretty strenuous. Adding any additional exertion seems like it would need a really good benefit to be worth the tradeoff.
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