Clays are for removing "high spots", contaminents, or paint overspray that adhere to the paint. They're basically a first stage prep before polishing or applying a "glaze" or paint cleaner.
I'm not too familiar with the "Imperial hand glaze " but I'm assuming that is is a sort of paint cleaner that hides swirls marks, thus filling any small swirl marks or light scratches.
Clay simply prepares the surface your about to work on.
Here is a good example of what the clay bar will pull off a car that had been washed twice prior to using clay, supplied by Johnlew:
I'm not too familiar with the "Imperial hand glaze " but I'm assuming that is is a sort of paint cleaner that hides swirls marks, thus filling any small swirl marks or light scratches.
Clay simply prepares the surface your about to work on.
Here is a good example of what the clay bar will pull off a car that had been washed twice prior to using clay, supplied by Johnlew:
