Fronts shifts. You don't control territory, without leaving man there to hold it. You can invade a planet, and kill any soldier on it; if you hop to another planet without leaving at least an infantry regiment to hold it (a lot more if you need to pacify it) than it'll just revert to whoever the population feels allegiance too.
I would say there are three levels:
Raids: you went in, completed your objectives, and bugged out.
Conquest: you came to stay, secured the location and assigned a garrison before moving on.
Denial: a middle ground, you deny a strategic location from your enemy, but don't have the logistical infrastructure to exploit it for your own needs at the moment; these are often strategic objectives that have little military value, like civilian factories, power stations, or even minor population centers. You may leave a garrison to maintain control of it, or simply destroy it so you want have to devote troops to holding it.