Something I don't get here.
A singer (if they've been singing for any amount of time) should be able to attend a session & size it up after LISTENING for a bit before jumping in with their voice.
Sessions are mostly very tempermental. They have their own personilities & it's up to the attendees to decied how they want to develop their relaitionship within that community.

I attend one session when I'd hardly sing a ballad, long or short. I love ballds but they love to sing along with the songs (short attention span, they want to sing on everything, whatever the reason, I don't know or care, it's there way) so I sing mostly chorus songs or songs that they can harmonize or sing along with or join in with voice or instrument & I love that too. Another session (strickly Irish & mostly instrumental) I attend when called on I'll sing usually something unaccompanied without chorus, they're mostly players not singers, they listen, enjoy but no matter how hard I'll try to get them to join, only seldom does any accompany or sing along.
Each has their own personility & it's up to each singer to ajust to the tone of the session. I'd love to have harmonizing & when I do get it I let it be know that it's been apprecated. There's one fellow at a session I attend that does a great job of it & we now will, when given the nod sing back up with each other but one needs to feel/suss out the session first. Easier done when it's your
regular session, harder when you're traveling about or at a festival go round but their'still a relationship that develops &
that should be acessed before joining in.

I don't run any sessions (thank God) but I'm a regular at a decent few. If I see someone singing along & the group/session leader doesnt catch on I sometimes inform the leader or just outright ask if they'd like to join in & lead something or go over & quitly ask if they sing & if they'd fancy singing one. If they're really good
keep asking them.
I'm very fortunite to be lucky enough to have some fairly decent sessions about me which makes life a whole lot more pleasant.
If you don't fancy a session that does long ballads or whatever the case may be don't go & then get pissed that it wasn't what you hoped for.
As for them that would sing & leave that's a bit like "cut & run", very bad taste & I can't imagine why anyone would even attend if that's all there is to it, no love of the song there.

Barry