SYSVOL missing?

I’m performing image backups on 2 clients. One of them has SYSVOL entries in the backups list, the other does not. The one that does is Windows 10, the other is Windows 8.1.

The log is similar in both, and looks like:

02/26/18 23:47  	INFO  	Starting scheduled incremental image backup of volume "C:"...
02/26/18 23:47  	DEBUG  	Backing up SYSVOL...
02/26/18 23:47  	DEBUG  	Backing up SYSVOL done.
02/26/18 23:47  	DEBUG  	Backing up EFI System Partition...
02/26/18 23:47  	DEBUG  	Backing up EFI System Partition done.
02/26/18 23:47  	INFO  	Basing image backup on last incremental or full image backup
02/26/18 23:47  	INFO  	Creating writable snapshot of previous image backup...

What is this SYSVOL anyway? Is it required for successful image restoration?