I think you might be right there ctbram, but I look at it a different way.
If you parent something, they are inseparably linked in the hierarchy. If you ever want to turn off that relationship, you can't. Now, a parent constraint you can key on and off as necessary. There's no inherent connection between them in the hierarchy, so you can create groups and other controls independently.
I'd use a parent constraint if you ever want to "unlink" the connection.