When you use credits to download a movie, it resides on your computer's hard drive. You can also transfer it to your tablet or phone.
You will be able to view this movie even when you do not have an internet connection and it will always be high quality.
When you stash a movie to our cloud, it resides on our servers (cloud). You can access it from any computer or internet connected device. However, you will need to have an internet connection. The quality of the streaming movie will depend on how good your internet connection is at the time you are viewing it.