If you have the Revisions enabled in the settings, anytime you save a file a revision is created in the workspace in .codetasty folder. The revision is created no matter what plan your account has, but can only be accessed if you have a premium one.
Example: You have a premium plan and share a workspace with your friend, he can edit the files and revision will be created but he can't access the revisions or restore them, only you as you have premium plan.
The Revisions can be displayed by clicking File -> Revision history or with shortcut Alt + R when the file is opened.