1) You understand how to use the Unix shell and everything else that goes into maintaining a Unix machine.

2) You have the time to do it. (This is what has always stopped me, FWIW.)

3) You are willing to spend money on a machine that has sufficient resources to be responsive when you use it but sits idle 99% of the time since you're the only user.

These obstacles are what drive people to SaaS, where they no longer have freedom to install arbitrary software.