While the purpose of this function is to apply glass to the selected Surface(s) to achieve a specific performance, there is also an opportunity to apply this glass type to this Revit family (wherever it may be on the model).
If this is not the intention, here is a second option to assign the new Glass Type to the selected Surface only. See Section 18.104.22.168.2 below for this option.
To control Glass Types on a different area of the project, new window or curtain panel types may be created in Revit under a different family name. This may be an option to help manage performance/specifications on different Surfaces.