When you are working with the application, basically, there are two way to close the application (kind of):
When you disconnect from the application, it will still continue to run in the cloud, but its time will be limited to 30 minutes (or only 10 minutes if you use a Starter account). If you take a look at Currently running you’ll notice the timer, which indicates how much time has left.
If you connect back to the application before the timeout expires, you can continue working with the application right from where you left. Application is still running in the cloud and therefore all the open windows, edits and changes will still be there.
If you do not connect to the application until this timeout expires, it will be killed and any unsaved work will be lost. Once again, if those 10 minutes run out all your changes and data will be lost.
It is always recommended that you close applications with File/Exit.