Maybe I will describe how it works now (it's implemented):
You have a pool of recruits they are divided into regular infantry (90%) and stormtroopers (10%). Each planet has defenisive priority (1-9) it's set automaticly (bored planets having 5, near borders 3, capital planet 8 and the rest 1) you can modify it manually between -3 and +3. Regular infantry is auto redistributed between planets based on these priorities.
Stormtroopers are more under your control, they are used for attack (you have "Drop stormtroopers" button after you win a space combat) also you can manualy garrison them on a specific friendly planet ("Deploy stormtroopers" button).
Overall it's not that bad, the distribution of regular infantry (defensive) is fine (the player basicly wants them on border planets). Also the "Deploy stormtroopers" order is fine, you can use them to reinforce a chokepoint planet. But the "Drop stormtroopers to invade a planet" button is super ugly and annoying.
The thing is, apart from "Deploy stormtroopers" order (reinforce a planet) you don't have any meaningful decisions and it's basicly a chore and a micro :)
Thoughts:
So, after stepping back and thinking about what I actually want as a planet I got these: the current auto distribution on troops (border planets get much more) should stay but without any priorities (me setting +1/-1 is stupid) instead there should be some sort of "reinforce this planet" marker, I put it on a planet and it gets more troops. Similarly I would prefer some sort of "concentrate offensive troops here" marker which I would put on a near border planet and then, once I send my fleet to get control over the enemy planet, my ground troops from the nearby "concentration" planet would auto launch a ground attack (not sure how exactly it should work, but I would definitely want to be rewarded for preparing the ground troops early, like moving my supply depots near the enemy, build some bases, concentrate troops, something like that).
I would also want some "deply some anti-riots troops here to suppress/prevent a rebelion" marker :D
These are my thoughts as a player.