Keepers with a large collection feed in the enclosure for convenience.
Keepers who have giant snakes such as reticulated pythons, burmese pythons, or anacondas, feed in the enclosure to avoid ER visits.
Keepers who have venomous snakes feed in the enclosure to avoid trips to the ER or morgue.
I have a few adult retics that are anywhere from 14-15 feet long and weigh in at 100-120 pounds. You are more than welcome to come to my place, pull any one of them out of the enclosure to feed it, and then put it back afterward. I just get all rights to the video footage because it's going on YouTube.
I would LOVE to find out just where you read that feeding in a separate enclosure is a good idea, so I can go debunk them. I have looked for the sites that advise it's a good idea and have come up with nothing.