Y'know--"Old Timey" catch-as-catch can jam sessions, in common with Celtoid "sessiuns" and Bluegrass jams are essentially masturbatory in nature. Them may be fun for those participating, but they can be a monumental drag for listeners. The biggest objection I've encountered to any and all of them is that they're boring, loud and tend to take over from any other music that may be present.

Good bluegrass is fine (though a bit rigid in structure for my taste); good Celtic music is fine; good "Old Timey" is fine. Too much of any of these tend to be not good. Good or bad, they're loud.