“Allowed Hosts” is white listing btw. You should leave it blank if you want more than just lemmy.world and lemmy.ml
And I wouldn’t say it reduces the load on those sites. It would kind of add to them in a way if you post from your instance or sub from your instance solo. If it’s just you on your instance, it’s barely a blip. May save them some photo hosting if you post.
SOME of the out of sync upvotes/comments are fixed in 0.18.1
I think it’s just a general situation. A lot of the “big instances” are having a lot of issues right now with federating correctly. Comments, counts, votes are all off on most instances it seems.
There are a few github issues you can find/follow. It’s supposed to be addressed a bit better int 0.18.1
If the bigger instance has to push/pull in data from you personal communities because they sub to it, then yes. 1 person not using your front end isn’t going to change much.