The thing I like about robocopy is that it does incremental mirrors so if files are already there and size and date are the same it doesn't overwrite them (unless you specify to)
Very useful for file server migrations. I migrated a files server across the WAN with this, took a week to copy all the data in advance (1.7TB 6 millions files) then on cutover weekend morning, kicked off an incremental mirror to update, copy and delete differences and it completed in 2hrs!
Now I backup up my PC to external USB drive once a week or so which I leave off most of the time, an incremental update mirrors all dirs in scope (130gb, 68,000 files) in just under 2mins.
Since it's not archived or compressed it's easy to verify the data is okay by opening photos and files etc. I've also had to restore from that several times.
Be warned though, Robocopy using mirror options can delete even faster than it mirrors, I've seen system admins wipe out huge shares in seconds, done a little damage once before too with it