There's no question that many people successfully run SBCs and are happy with them but here's some of my biased reasons why I don't recommend ARM based SBCs like the pi, HA Green, HA Yellow, HA Blue, etc for running servers.
- They have a poor price performance ratio
- Some need a powered USB hub if you want to reliably use their USB ports, for example for a external SSD [2]
- Their internal storage sucks [1]. SD cards corrupt easily
- USB boot can be finicky and likely has to be configured:
- You need a HDMI adapter or USB C cable and a serial software to debug some of them
- You can only run specialized distros on them and hence can't easily boot just any live iso to troubleshoot or test something [3]
- You're limited in what you can run (ARM) and debugging tends to be harder
