The cons are that you suffer the worst of both worlds, you get stuck in traffic as if in a car but still get cold and wet as on a bike!
The pros are that yes, pretty sure you can drive a trike on a car license so long as its under a certain weight (and most trikes are), you can carry more gear/people/dogs etc etc than on a bike and they look ALLOT more fun to drive than a car.
Never driven a trike myself but thought about allot recently as a means of taking my dogs out with me, maybe one day.