Founding a successful new conference is extraordinarily difficult. As a conference founder, you must manage to attract a significant number of good papers—enough to entice the participants into participating next year and to (generally) to grow the conference. For someone choosing to participate in a new conference, there is a very significant decision to make: do you send a paper to some new conference with no guarantee that the conference will work out? Or do you send it to another (possibly less related) conference that you are sure will work?
The conference founding problem is a joint agreement problem with a very significant barrier. Workshops are a way around this problem, and workshops attached to conferences are a particularly effective means for this. A workshop at a conference is sure to have people available to speak and attend and is sure to have a large audience available. Presenting work at a workshop is not generally exclusive: it can also be presented at a conference. For someone considering participation, the only overhead is the direct time and effort involved in participation.
All of the above says that workshops are much easier than conferences, but it does not address a critical question: “Why run a workshop at a conference rather than just a session at the conference?” A session at the conference would have all the above advantages.
There is one more very signficant and direct advantage of a workshop over a special session: workshops are run by people who have a direct and significant interest in their success. The workshop organizers do the hard work of developing a topic, soliciting speakers, and deciding what the program will be. Reputations for the workshop organizer are then built on the success or flop of the workshop. This “direct and signficant interest” aspect of a workshop is the basic reason why franchise systems (think 7-11 or McDonalds) are common and successful.
What does this observation imply about how things could be? For example, we could imagine a conference that is “all workshops”. Instead of having a program committee and program chair, the conference might just have a program chair that accepts or rejects workshop chairs who then organize their own workshop/session. This mode doesn’t seem to exist which is always cautioning, but on the other hand it ‘s not clear this mode has even been tried. NIPS is probably the conference closest to using this approach. For example, a significant number of people attend only the workshops at NIPS.