Are price book associations with the default price book ever used?

Summary:

We currently use price books and upload price book associations nightly, including the default price book.

However, if a part has no price in Parts, but there is a price associated with the default price book, the part's price is still used.

Does this mean there is no value in creating price book associations for the default price book? We update prices for Parts nightly, so associating them with the default price book would appear to be redundant and moot. Additionally I noticed there is no Expand button available for the default price book in the Price Book Administration List, further evidence that associations in the default price book are never used.