For example in a project we select an element like a wall and then interact with the dimension value (permanent or temporary) to move it. If we select the dimension first we end up in the Dimension Text dialog instead. Revit thinks we want to override the dimension with text or add a suffix/prefix.
In the family editor however we can select a dimension that has a parameter associated with it and interact with the dimension value directly to change a referenced element's position.
Just remember, It's the same only different or It's always like this except when it isn't.