The ShortPixel image optimization/compression plugin can really help with site speed by making your images smaller and more efficient, without sacrificing visible quality.
By default, ShortPixel stores backup copies of original, unoptimized images on your server. These are very useful when you're first starting to use the plugin, as they allow you to compare the original to the optimized version and quickly revert in case you want to try different settings.
However, once you're happy with how ShortPixel is performing, you should retain your own backups of the full, unmodified originals (for example, on your own computer or some other backup solution) and disable and remove the backups that ShortPixel stores on your server. If left enabled, ShortPixel backups can eventually consume a significant amount of diskspace, which can lead to site availability issues.
Clearing Out Existing Backups
Clear out the backups folder by going to Settings → ShortPixel. Click on the Statistics tab, and then the Empty backups button. This will immediately free up the space those backups are using.
Click the General tab and uncheck the Save and keep a backup of your original images in a separate folder button.
Keeping Backups Enabled
If you'd like to keep the backups on your server, and want to be sure you have enough storage to do so, contact us and we can give you a quote for increasing your disk space if necessary.