As far as I know, the reason spawn chunks stay loaded on a server is because it's a high-traffic area. Players keep coming to the spawn area for various reasons, and when they enter the chunks load up. In order to reduce the amount of time spend loading and unloading those chunks, some servers are designed to delay or prevent chunk unloading in that area in case someone else comes along in the meantime.Well, since I'd rather be building than researching, I just moved [am in the process of] my mushroom farm, crucible lava gen, and sludge processing, to the nether...when I noticed something. My spawn chunks are unloading? I didn't think that was possible. I looked into this about a month ago and there doesn't seem to be any real definitive information other than spawn chunks exist. Anyone have any info on this or is it something specific to AgS?
BTW only reason I knew is I cannibalized my chunkloader for a couple spot loaders and then had issues when I wasn't getting any water through my Tesseracts in the Nether. Dropped a spot loader at my Overworld water works and problem solved. Supposedly spawn chunks are 12x12 or 13x13 around spawn. My Overworld build is wholly contained within this area.
But in single player, even the world spawn chunks will unload if you aren't there to keep them loaded.