I have Time Machine back up my system drive. I haven’t noticed any effect on system performance.
I use Carbon Copy Cloner to back up my media RAID however because I don’t necessarily want to back up every single file that is on my media drive. I use Event Manager X and backing up via Time Machine can cause redundant file backups, for instance if it backs up while a project is active and then again when the same project is inactive you get duplicate backups.
It’s not automatic but I prefer not to be on automatic when it comes to media files. At the end of the day I use Event Manager X to take all projects and events offline and then back up with CCC.
anickt