The thought of Retaining a host is more geared towards keeping an already Heavily mutated host (for example; one that you've added full Protective Covering to, or a level 3 health upgrade, or so forth) and exchange for a more discreet one - one with a camouflage cover and neurotoxin 'needles'. So on so forth.
Simply put I'd like to be able to keep a super-soldier in storage for when stealth has become moot due to how much the humans want me dead. For the most part anyway.