What is it? It is a speed / rescue boat. Quite a large one with a crew member who controls the boat and there are benches for even more people. You can also use it as a fishing boat. Actually, there must be a surfer or a shark or a few buoys.
Why did I build it? I had the boat itself (the white bottom) and I wanted to do something with it, and now it is a speed / rescue boat.
Why do I think this would be a great LEGO set? It may be a bit small in terms of parts, but I like how it looks. What I also really like about it is that it floats and that makes it even more fun.