Re-roofing is permitted work
Replacing a roof covering requires a permit from the building department with jurisdiction over your address — LADBS inside the City of Los Angeles, your own city elsewhere, or the county in unincorporated areas. Small repairs below the local threshold generally do not. Your contractor should be able to tell you which applies and pull it under their licence.
The inspection is a free second opinion
A permitted re-roof is inspected by someone who is not paid by the contractor. For most homeowners that is the only independent look the work ever gets, and it is the strongest practical argument against an offer to skip the paperwork.
Unpermitted roofing follows the property
It surfaces during sales, remodels, and claims, and it becomes the owner's problem years after the contractor is gone. A permit-free discount is a deferred bill.
Fire-hazard zones add requirements
Parts of LA County sit in designated fire hazard severity zones, where the roof assembly must meet heightened requirements. If your address is in one, the permit process is exactly where that gets checked — another reason not to bypass it.
Frankly