If you can afford the extra space, the island exhibits offers the least restrictive show rules of all the booth space layouts. Key features include aisles on all sides, allowing access to the exhibit from all directions. Another way of saying it is that you have no neighbors, you are an island. Because there is no one else that is competing for sight lines or visibility you are able to enjoy the maximum allowable height offered by the show organizer in the exhibit hall. This includes structures in your space from the ground up, or overhead signs connected from the ceiling.
The maximum height is usually much greater than the linear exhibit limitation of 8’ and is usually from 16’ up to about 25’.  If you plan to exhibit in a space larger than a 10 x 20, you should give serious consideration to the 20 x 20 island exhibit before opting for the 10 x 30 or 10 x 40 simply because of the advantages of the additional visibility, position on the show floor, and least restrictive show rules.