You get raw access to the underlying filesystem. Notice how the website and the filesystem are in sync. Editing your filesystem is identical to editing your website.
Here you can see how images in a gallery are stored on the Boomla filesystem. Manipulating the filesystem is identical to editing your website on the graphical interface. Here we directly remove an image file and upload a new one.
You can clone your website to create so called secondary branches of it. Changes made to these clones are not visible on your public website, the so called master branch. You can then either drop or publish your changes.