Why & how to separate feeding from sleep?

We are planning on sleep training our 4.5 month-old soon for nights and then will work on naps. He currently exclusively contact naps and is (breast)fed to sleep for both naps and nights. Basically for naps we “sleep, eat, play, eat” and repeat since he generally eats a bit more when he wakes up. Just wondering if it is absolutely necessary to separate eating and sleeping or if it is okay to feed then put down immediately while trying to foster independent sleep? (Instead of keeping him latched and waiting until he’s completely out before attempting to put down, which is our current status and is getting old because he frequently wakes up and then we need to start over!) I always see advice to separate the last feed by 20-30 min before bed… but why? Has anyone else with a fed-to-sleep contact napper successfully switched up their entire routine for both nights and naps? Any thoughts and advice appreciated!