I imagine it means the same thing as being a protectorate but your planet is in the Pact Worlds system; you get representation in the Pact Council, but they're a non-voting representative just their to advocate for your world's needs & attempt to sway full member worlds.
At the risk of bringing real world politics into it, one could think of them as similar to the territories of the US like Puerto Rico, Guam, American Samoa, or even Washington DC; they each have a representative in congress, but they don't actually get to vote on any issue.
Aside from that, even with the benefits of drift travel, there is a certain autonomy that comes with distance and just being "out of sight, out of mind".
There is a SFS scenario that discusses this some, called, appropriately, The Protectorate Petition.