Maintenance fed just means that when an animal is a few years old and out of it's 'growing' phase, you basically feed it enough to keep it healthy but not get obese. Problem with captive snakes especially boas who have a slow metabolism is that that 6' snake kept in that 4x2 cage has no real room to move around like in the wild where they would have to climb, swim, crawl and basically hunt for food and possibly go months without finding it. They would burn calories looking but in captivity, they dont need to do anything except sit there like a bump on a log waiting for that clockwork feeding to come around.
Same goes for a BP. They usually hang out in termite mounds and abandoned dens. So they literally hav2 choices, wait for dinner to wander in and pray they catch it or go out looking for it. In a cage, using energy to go out looking for dinner is pretty minimal since again, most people use very small cages for them. So they wait around. Well in the wild, I would imagine that dinner doesn't come wandering in like clockwork every week or 2 and is the optimum size. So you basically maintenance feed to basically do what mother nature does, only artificially.
And some guys will actually lower temps and quit feeding altogether for a few months for boas to simulate winter. Also heard its not bad for them to do that. My boas all live in an eternal summer though but I do tend to stretch their feedings out more in the winter. And for my BP, well she regulates herself. Last winter she quit eating for 6 months but managed to shed, poop and grow during that time haha. My boas do that too. In winter when I feed them less, they seem to shed more and grow more haha.