What are the pros and cons of a client state based sci-fi empire?
I'm working on building a sci-fi world and I had an idea for how to cut down on the sheer amount of bureaucracy that a massive (say, 200 planets) empire would require. What if the central government ran a system of client state like planets instead of directly annexing each of their conquests? In this set-up, the conquered planet or civilization would be allowed to have self-rule under a new government formed by the empire. The client states would be allowed to have land-based militias, but no space-fleets. The central empire would set a specific quota of tax and manpower for the client to give to the state and army, respectively, then leave the government on their own to figure out how to acquire these things.
The pros I can see off are that it makes bureaucracy much easier for the central empire and can potentially make the transition easier for the conquered worlds. The primary issue I see is that these client states could be prone to rebellion if the central empire ever grew weak. Thoughts? Am I missing something obvious here, or does this seem practical?
Edit: Added more information
Thanks to @nullpointer for pointing out a few things I failed to include. The FTL travel of the universe operates on a jump-drive technology with relatively limited range (say, 2 lightyears every day). The exceptions exist in areas where natural or artificial wormholes have been set up. 302
These wormholes require a lot of resources and time to produce, however, and rarely exist in these hypothetical client states. The Empire in question is (at the time the story takes place) working on building waystation wormholes to make transit easier, but right now travel from the home planet to distant client states take weeks or months. Communications in this empire can only travel as fast as the fastest ships, so they're locked to about the same timeline.
Finally, a bit about the empire's motivations. On the home planet, political careers are driven by military successes, i.e. a candidate has to have won x many victories to be eligible for x position. Because of the wormholes near their planet that connect to other planets, they discovered a few other civilizations before the jump drives or even militarized spaceships. This allowed the dominant state on the home planet to finally complete their hegemony without concern for a collapse of their political system and transition into a spacefaring empire. The larger civilizations (this empire included) of the galaxy nearby retain a mutually lucrative trade route that generally keeps them from conquering one another. That leaves smaller, typically less advanced civilizations as targets.
If the general agreement is "yeah, this should work fine", then here's a secondary question: would the empire want to maintain garrisons (either space or ground-based) in client states, or would that cost too much/lack justification? 145