I have tv shows music, I install all my games to this drive to free up space on the os drive. I also have everything from my sisters computer in terms of photos videos and stuff we took and there's over 100gb of that.
Music about 20GB
TV/ movies about 600GB
photos videos we took about 100GB
Games about 50GB
backups for computer repair clients 150GB (this will probably end up going on an external for convenience)
so a total of about 950GB is used and being that storage is so cheap why not go with more. If I buy less then turn out to need more I'd be out of luck.