When you use this functionality, there are a few things you need to keep in mind:
(1) The incremental backup will capture the difference between the source and destination, but will NOT delete files in the destination that were subsequently removed from the source. So, over time your destination (i.e. backup) will grow larger than the source. To address this issue I have a scheduled run of Syncback (freeware backup software) on my PC once a month to reconcile the difference between the two volumes.
(2) The backup functionality has some issues with file names containing certain special characters. If a job encounters an issue with the file name, the job will fail. This issue is somewhat rare, but has cropped up from time to time. The error does not flag the offending file name, so you'll have to do some investigating to isolate and rename the file.