If you are in the middle of a painting project and need to stop, you can wrap your brush/roller in aluminum foil & put in the freezer. When you are ready to start again, simply remove the foil and allow about 15-20 mins. to thaw. Your roller will be ready to go!
This saves a lot of time (and paint) by not having to thoroughly clean brushes/rollers each time you stop, and only when you are completely done with the project or when using a different color.