What I would give to see all client environments have just disk monitoring to prevent them from filling up and stopping the show...
There are fairly simple scripts that can help here. Scan for xx space, send an email / page / net send. The other thing to do is create placeholders that give you time to respond: https://voiceofthedba.com/2014/12/01/creating-placeholder-files/
I love this. I use this tactic frequently in Linux environments to reserve space. Also wrote custom login scripts such that if there was low disk space, restarting the server would clear out a file or two to get some space back to work on the system. Not a frequent issue any longer though.
To reserve disk space for your database files to grow, why not just initialize or re-size the files to the appropriate size?
Creating placeholder files might be confusing to another DBA who is trying to resolve a disk space issue, but certainly make the file name descriptive in a way that someone else knows they can safely delete it if needed.
"Do not seek to follow in the footsteps of the wise. Instead, seek what they sought." - Matsuo Basho