Mimbranes kept at high feeding levels noticeably make the body parts they are attached to bigger and more engorged, so you get swollen lips, breasts, genitals, butts, hands, and/or feet. It is a wholly cosmetic effect, but you can like or disike it, according to your looks preferences. I do like mimbrane symbionts, but I noticed one of the biggest headaches in their management is how different sex acts may often feed certain mimbranes but not others, and so annoyingly scatter their feeding (and trust) levels all over the place. Therefore, once I get a full set, I use save editing to syncronize their trust and feeding levels, and I make a routine of feeding all of them at once just after a new day starts, so the syncronization lasts.
Once the attached mimbranes reach maximum feeding (and trust) and Steele got maximu level and stats, I usually prefer to keep them in this state as long as possible, since this frees me from almost all concerns about their management. You can do this by using rest (outside the ship) instead of sleep (inside the ship) to refresh the PC. Once Steele gets maximum level and stats, you only need sleep in rare circumstances (e.g. to remove physical exhaustion status effects from Paige's yoga) and I don't care much about reading the dream and 'sleeping with crewmembers' scenes all the time. The only remaining concern is after a few days of not getting feeding actions, mimbranes start sending 'hungry' messages even if they actually are fully sated (nonsensical if you ask me; I never understood if it is a bug or the game working as intended with a logic that escapes me), therefore every so often I use save editing to reset all mimbranes' days-since-feeding stat to 0.
'Porn biopunk space opera' is more or less how I'd usually define this game in fiction genre terms, given its focus on erotic-oriented bioengineering (working with porn logic) in a far-future interstellar setting dominated by mega-corporations with fairly 'soft' levels of sci-fi hardiness. Oh, and the annoying overabundance of futas, with every second feminine character and their humanoid pet seemingly having a craze for getting male genitals in the far future to gross this anti-futa player (genital slits would definitely help my comfort a lot, but unfortunately they are woefully underused by NPC and non-existent in game art), but I suppose catering to the author's fetishes is the inevitable price of getting a good game.