Dreamy clouds can be exactly that -very dreamy - as they give you extra moves!
When you come across clouds, they will have a number on top (+1, +2, +3, etc). Make a match of 3 or more next to a cloud and receive extra moves (+1 gives 1 extra move, +2 gives 2 extra moves, etc).
Clouds can also be hiding underneath some blockers, so keep an eye out for them, especially if you need those extra moves!