This is all pretty obvious when you really think about it.
One way to think of content types is to visualize the contacts on your mobile phone.
Base configuration: The base configuration of a content type defines the default behavior and properties of the content type.
Examples include whether or not a newly created item of content has the status of by default; or whether or not a newly created item of content is associated with one or more menus.
Content types have a collection of field references (or links) to the list columns which get updated, but the links themselves have their own set of properties which override those set for the list field.
This means that if you run the Power Shell snippet above, any existing content types which reference that field will continue to show the field on edit forms.