I had two Dropbox accounts.
One I use personally with nearly 1TB which I access almost daily... I'm really considering moving it to iCloud or OneDrive since I have both already as part of my iDevice backup policy and Microsoft Office 365 respectively... Both lying largely empty.
The second, account I had managed to max out by making multiple referrals to the students of a school I run, since I used it as the primary means of disseminating course material and receiving submissions.
I have now had to say good bye to that account since they limited it to three devices and when I upgraded to Mojave, dropbox asked me to reconnect, which I couldn't. If they assumed I would upgrade to a paid account, they assumed wrong. My school and about 50 or so students moved to an in-house server solution as of May this year and many of them will no longer be renewing their subscriptions to Dropbox.
Sometimes nickel and diming can come back to bite you in the arse.