I don't claim that the following is correct but that is what I think the differences are.
A Control can be used like a template which you then can adjust to your needs. Compared to a real type definitions the instances where you use that control won't automatically update when you change your control.
A Strict Type Def. compared to a Type Def. won't allow you to change for example the color. If you want to change the color you have to change the Strict Type Def..