Integration with Dynamics Customer Insights (DCI) appears to use the DCI's primary key in the Name field for the Segment entity.  This is pretty poor practice and means that:

• The segment name has to adhere to limitations imposed by DCI (e.g. the name can't have spaces)


• The segment name can't be changed in D365 after the record is synced to DCI (even when stopped)
  
  [See D365Mktng: Segments: Can't rename even when Stopped once put Live]


• If Segments are set to Draft (to enable a name change in D365) once put Live again they are orphaned from the original DCI record


• Unlike the vast majority of CRM records two Segments cannot have the same name

If this must be done (rather than use some GUID behind the scenes) please hide this field and provide a Name field that can be editted in the way CE/CRM users are used to being able to.