Depends on the workload, really. 120 users using small services? probably. 120 users sharing large files or bandwidth heavy stuff? Doubt it. Also a lot of enterprise hardware is about reliability. Multiple PSUs, NICs, more robust hardware for constant load/network traffic, etc.

Sure, a gaming rig can handle it until it can’t. Another question is what happens when the box crashes? Is the business down until a new PC is built and restored from backups?

A small business can probably afford two PCs, but scaling up and up eventually becomes a lot of trouble and space.