This is commonly done simply because there is not usually enough bandwidth to send a full disk image regularly to an online backup service.

Here's the proper procedure.

Do a regular full image backup on site using RBackup's built in Full Image Backup backup set. Set up a scheduled task so it launches nightly or weekly. 

Then also do file backups using RBackup Online Backup. Launch the image backup BEFORE the RBackup online backup is scheduled to launch.

This will give you an up to date image to quickly restore from.

At restore time, restore from the image first. Then start up the RBackup Endpoint and restore all the files that were backed up since the last image backup.

This should restore your entire drive quickly.