Hi, I'd just like to expand a little on what Chris Cai said above. These FontCache-S-*.dat files are created by the Windows Font Cache service. I am the developer for that service, and can confirm what Chris said above. It is safe to delete these files.
The service will simply recreate them as needed.
Just to confirm, the problem you're observing is with the sheer number of files, correct? In other words, the 50+ GB you mention must be the total size for all the files. In Windows 8 and 8.1 each file should be 8MB so to reach that total there must be thousands
of these files.
As you've guessed, these files are per-user, so if many people log on to a server you could end up with many of these files. Unfortunately, the Font Cache service does not automatically delete old per-user cache files so for now I'm afraid you'll have to
work around this on your own. For example, you could create a scheduled maintenance task that automatically deletes all the FontCache-S-*.dat files if their total size exceeds a certain amount. This is a safe workaround.
I'm investigating handling this kind of maintenance automatically in the next version of Windows AFTER 8.1. I'd be interested in any input that might help me decide on a reasonable clean-up policy. E.g., should it be strictly time-based or should there also
be a cap on total disk usage? Do the servers in question tend to have just a few regular users and lots of infrequent or one-time users? A time-based policy might work well if that's the case. As far as space, what would you personally consider excessive and
is this the sort of thing you'd want to be able to configure?
I hope this information is helpful, and thanks in advance for any input you may have.