Stellaris II: I, For One, Welcome Our New Robot Fungus Hivemind Overlords

[Artanis]

It does make sectors by itself now, yes. It seems to be based on the star clusters on the map. I currently have three planets and three sectors. BUt I'm not sure if sectors actually do much except need separate governors.

IIRC, they changed their minds and removed the thing about star clusters determining sectors. As far as I can tell, what it current does is, if you settle a planet that is not in a sector, it will create a new sector extending 2 jumps outward from that planet.

And yeah, sectors don't do much beyond making you hire more governors.