A picture is worth a thousand words and perhaps a lot more dollars if you're an event planner. When trying to land a client, you can do your best to verbalize your vision or describe details of past events, but a photo will always do it better and faster.
A camera is great to have on hand as a reference tool, as well. You can take pictures of potential event spaces, take photos for an inspiration board or photograph possible purchases and their prices for reference later. A CD full of photos from an event is a great parting gift to a valuable client, and a digital camera makes it happen in a few clicks. The great news is that digital cameras are getting smaller, higher in resolution and cheaper every year.