When you start using the Create video editor, you may see a popup like this under the address bar:
The editor uses your browser's cache as well as some temporary storage on your computer to allow you to work with your files quickly. This temporary storage space gets automatically cleared by Chrome on a regular basis, so you don't need to worry about losing space on you hard drive. Clicking "Allow" is important for the editor to function correctly.
Create only stores the working project files that are required for you to edit your project.