A nightly crew keeps a kitchen serviceable. It does not get to the high surfaces, behind the wheeled equipment or through the built-up grease on equipment exteriors, and it is not supposed to - there is no time in a closing shift to do it properly.
Deep cleaning is the periodic reset that keeps the serviceable kitchen from quietly falling behind. Grease migrates. It collects where nobody is looking, and where nobody is looking is exactly where an inspector looks.

Kitchen surfaces and countertops cleaned and degreased, edge to edge.
Walls, tile and floors scrubbed and degreased, edges and baseboards included.
The outside of kitchen equipment cleaned and degreased, including accessible cold stations and reach-in units.
Safely accessible ceiling areas and overhead surfaces dusted and wiped down.
The exterior and surrounding area of the floor drains, which set the smell of the whole room.
Behind and around equipment that is on wheels and can be moved safely without disconnecting utilities.
Not included: internal equipment cleaning, hood or exhaust-system cleaning, ventilation or ductwork, grease-trap servicing, condenser housings, equipment disassembly or mechanical servicing. We do not provide hood-system compliance certification.
Book it far enough out that anything the walkthrough turns up can be fixed before the inspector arrives, not after.
Deep cleaning wants the kitchen to itself. A dark day or a quiet stretch gets you a better job for the same money.
An initial reset sets the baseline. After that the recurring visits hold it there instead of fighting a backlog.
Deep cleaning is quoted after a walkthrough, because the condition of a kitchen is not something anyone can describe accurately over the phone.