Cover comps are for client proofing

A cover comp is a mockup of your cover - it helps a client picture the finished product, the material, spine and title, as part of proofing. It's not meant as a production file: most vendors build the physical cover from their own templates and specifications, so check with yours before including it in production files. The cover does still export at full print resolution like any spread, so if you print covers yourself, or your vendor accepts custom cover files, it's ready to use.

Starts at 0:03 in the covers videoWatch on YouTube