If you're organizing a conference, you'll need more than a simple assembly hall or space with a lot of chairs. The hall should be located in a building with an attractive façade and plenty of parking - participants in your conference will only be with you for a day or two, and making a good first impression is vital. You'll most likely need equipment for projecting video and sound (and you may need simultaneous interpreting capabilities). You may also need a separate space for registering participants and coffee breaks.
Dance is about movement. The venue for this kind of event should be spacious enough that everybody participating can feel free and not have to worry about bumping into one another. You might want to check whether it includes a changing room, shower, and toilet.