From making it to selling it
The panel is priced. The installation is not.
It starts as a rectangle with a logo. Then the customer asks for another artwork change, the small lettering takes longer to weed, and the mounting surface needs more preparation than the photo suggested. The material estimate was right. The job became bigger around it.
A finished sign is a sequence of work: design, printing or cutting, finishing, mounting, and sometimes a trip to site. Square footage helps with the panel and film. It cannot describe every hour needed to put the result where the customer expects it. Keeping those parts visible makes the next quote easier to explain and easier to change.