I think there pretty much always is one. I found, in my VERY limited experience at CSR that it doesn't have impact on crowd but might have impact on "feel". We stated once and our stay overlapped two convention/conferences with about a day between.
# 1 was a respiratory therapist conference. The attendees were fun. Many therapists are women, there were a lot with families. They enjoyed the pools (you could pick them out discussing sessions while kids splashed around them). They were only easy to spot on park busses or the pepper market if they carried a drug rep tote bag, etc. Typical Disney goers, also getting some education credits. I may be biased as a nurse but I know our job is stressful and when the classes are over at a conference, hospital types love to let loose and have fun!
#2 was a financial/ business conference. Mostly men, mostly alone, without families. They were very professional and business like. Suit and tie for sessions, that's how you would see them at lunch and even traveling on busses- like DTD for dinner. By this time in our trip it was cooler and rainy... We didn't even use the pool so I don't know about them. We sat across from 3 guys in their suits in the way home from DTD and it was clear that the pixie dust missed them. They criticized Disney business practices, etc. analyzed transportation and dinner, then turned back to debating office politics. It was a bit of a bummer since we experienced it a couple times with that group. Too bad they didn't bring along spouses and kids and relax a bit. I suspect they were the serious career types who may not be married? Maybe just a mistake on the part if the conference hosts to pick a Disney resort and not Gaylord or something? I actually overheard some grumbling about "having to come to WDW" They were also frequent flyers who complained a lot at checkout/ airline check in. Many tried getting on our bus to the airport which was a couple hours earlier than the one they were signed up to take. (If I remember that correctly and if I'm use ing correct words).
I suspect most conferences are like the first, not the second.