Of course, turning up at a pub is not a guarantee that there will be any space. The Scratch have often found people eating meals in the corner we head to. Sometimes they finish and move on. Other times they enjoy the crack and stay there, maybe joining in. Thankfully nobody has taken offence yet.
Extra mudcatters in the pub might make it difficult for ALL to fit in a limited space, so we could end up spread into more than one part of the pub, but that can offer the opportunity to chat, which does not present itself when there is wall to wall song or music.
It is never the intention to spoil someone else's fun, but an open pub is a "posession is 9 tenths" situation, and we could just as easily be the later arrival. I don't see a problem jigsawing into someone else's session should there be one already going, as long as people are sensible and don't try to crowd out and take over.
Personally I see a Mudgather as an opportunity to meet and have a chat, and time away from any singing can be more valuable than that spent listening to a performance.
Quack!
Geoff.