To add to what Sanjay has said... bringing a small tank to display has become popular mostly due to zoanthid / acan selling I'd say. It is hard to get $50 a polyp (which is ridiculous, but that's another story) when the buyer can't see the colors. I've seen some pretty sweet displays hauled around to the bigger swaps.
In my experience, if you have the normal variety of corals that most people can picture in their heads, you don't need a tank. Nobody needs to see a frag of green slimer, orange monti, pompom xenia, etc. If you are bringing things that aren't all that common, or frags of corals that have multiple colors that can't be easily described, a small tank with appropriate light will help you.
S !