We tend to think of fields as either Required or Optional but that’s not quite the whole story. CRM may refer to a field as System Required which is a required field that can not be changed to be optional. Some of these are obvious… owner, status, etc. But a few may catch you by surprise such as the Customer field on the Case entity.
There are also Business Required fields. These types of required fields may be changed to optional if it is not something you are interested in enforcing. Worth noting that CRM’s metadata may refer to these as Application Required.
What about that Business Recommended setting you say? That adds a little blue indicator next to a field that you may want to have filled in but it does no enforcement of that.