Conferences use twitter hash tags to promote to the audience within the venue, as well as those around the globe that couldn't make it or just would like to know more about the event, it's speakers and general content.
Hash tags ( eg #creativephotos) are used by twitter users to quickly search on all tweets that contain the hash tag that has been chosen by the conference organiser. As more and more people tweet from a conference and include the hash tag then a growing list of tweets can be viewed that directly relate to the event.
A good example of where using a professional photographer is beneficial to your conference's social media output, is when you need to tweet a photo of a presenter (along with the hash tag) before they have finished and sat down. You could snap it on your mobile phone - but this is rarely good enough to convey a well run event. I would have a series of professional looking photos within the first few minutes, upload them to my online gallery and they would then be available for tweeting.
Social media is such a fast paced, instantaneous communications tool. People do expect updates to happen quickly and often. Momentum is the key here. Keeping updates flowing throughout the day will build a real buzz around your event.
Processing my photography at events in this way provides your communications team with a constant flow of relevant and topical imagery.