I know what I like. I like Will Fly's version. At my Lower Stoke Winter Sings (now terminated because the pub is a UKIP pub and the landlord a UKRAPPER) we went one stage further and invited instrumental accompaniment as well, unless the singer expressly wished otherwise.

I have been to other primarily song sessions where that was the rule too and had some very positive experiences when singing, a notable example being when a rehearsed arrangement (with my usual tenor) of a shanty in B we were delighted with an extempore blues-style guitar accompaniment coming from behind us. It really gave the song wings (fortunately not Paul McCartney's Wings).

Also, although I am really a very limited mandolin player, I have three times been told that my ad-lib accompaniment was a definite plus, once by a local professional performer, and once (to my great conceit) by an internationally known professional shanty singer.

On the other hand, if I find I am not getting it right I usually shut up pretty fast (which may surprise some here)! Once I was accused of "noodling" (a misuse of the term in my view) when accompanying a singer. I hold that "noodling" is what guitarists do between songs, playing random notes or phrases or just something they like the sound of, so stopping the next song starting.

I am lost for a suitable expression to describe what has happened to me twice - a song or an introduction to a song has been started and then a banjo-player (a well known and very loud tenor player, with, incidentally, a criminal record and who purports to repair, but wrecks, guitars) or a professional "entertainer" with a penchant for unfunny jokes badly told, loudly chimes right over and so stops the song.