Conference photography requires a photographer that has a unique skill set. You have to be invisible 90% of the time, be capable of working with available lighting (no flash here) usually the most challenging you will come across. You will need wide angle Lenses used in landscapes and telephoto lenses used by sports photographers and everything in between.
Some conferences require you to take control of the 200 delegates, get them to move to a location for a group photo and keep everyone smiling in the process.