It works well for companies (in the SME context)that have staff working remotely.
If you have 20 staff all in the same office and just want basic file sharing, SharePoint is probably not your answer.
If running SharePoint internally you also need to take into consideration maintenance, patching, reliability and disaster recovery. All much easier with a file share if you don’t need the more advanced features of SharePoint.
As other’s have said, it works well for document version control. I’ve implemented it a few times for this reason.