If the Folk Club is held,in an already existing bona fide Club i.e. a Rugby Club (and not a pub) in theory all persons entering the Rugby Club should be Members , or signed-in guests.
Making the folk people form a Folk Club within the Rugby Club, helps to get round this archaic rule - a rule which the cops can enforce on the organisers and the attendees if they so wished.
It works well at Guisborough Rugby Folk Club, but if in doubt check with them the "ins and outs " of this system, as ,I believe I have over-simplified the method above.
Otherwise , being members of a Folk Club, getting reduced or preferential ticket prices than an non-member,as a bonus for committment to the Club is fine for me.
I wish soccer Clubs would follow this example.

Cheers

Betsy