Solaris @ChristopherKhawand To be fair, more and more shared hosts provide SSH access enough for maintaining a Flarum.
The problems will most likely arise once you reach a certain activity level.
Worth to know though, is that while it is easy to follow a guide for setting up a VPS, maintaining one can be tricky if you don't know enough.
This could mean the site would run slower on a badly configured VPS then on shared hosting.
Additionally, a badly configured VPS could be insecure, which can hurt you, and your communities visitors.