Can someone answer - what's the point of publishers?
what do they do, what do they take, are they worth anything?

I have thought about an answer to this one for a bit.
I had a publisher for a while with a lot of contacts, and that worked for me, as I got given a lot more writing commissions for TV etc, which I would not have had without them. I also was paid in advance which was useful, however, these days I just register works with PRS/MCPS myself, but then that leaves yourself with all the promotion to do.
I had a lot of doors opened for me at record companies by my publishers, which would have been closed had I tried to get the meetings myself, so in that instance it is worth it. I think that IF you are embarking on a professional route for the first time , yes get a publisher,(and get an advance) if you are not , D.I.Y.

MK(no hits whatsoever, but a number one video theme tune once, which I would not have had without my publisher!)

yes songwriter you are correct.I own a publishing company and I do fuck all.ascap and mcps collect all monies and I split 80/20 with band which I think is a great deal for band.I do of course lay out money for advance but so what.

... my early ones were 50/50 with advance! But I was skint!