Setting individual cap size on Time Machine storage on OS X Server I help manage Time Machine backups via OS X Server for my office running on El Cap 10.11.6.  Is there a way to manage storage for individual users on the server side? Right now I have it capped out to 750GB, however I ran into a user that has a TB drive.  I don't want to arbitrarily up the cap to 1TB, I need a way around this dilemma, so I can custom manage each user according to their needs.  I researched this and want to learn more about tmutil, but didnt see a cmd that is applicable.
You could use Profile Manager in order to do so and setup individual limits per machine.

Login to Profile Manager and register your device (i.e. by downloading the profile to it) if not already done. Then you should be able to setup every single fine grained setting you want for that device without the need of any terminal-hacks or external tools.