A release records what the person in the picture has agreed to: which images, for which uses, in which media, for how long and in which regions. A friend who models a jacket for a small shop, a customer who sends a photo wearing a product and a professional booked through an agency each need a clear agreement before the image is used commercially. Agencies usually supply their own contract with the permitted uses spelled out.
The scope is where problems arise. A release for a website may not cover paid ads, print or a marketplace listing; a time-limited booking can end while the images are still live; edits such as placing the person in a new scene or changing their body may fall outside what was agreed. Some marketplaces ask sellers to hold the model's permission before a face appears in a product image. Keeping the signed release with the image files makes a later question easy to answer.
Generative tools add new questions. A real person's photo used as a reference, or a face carried over into a generated image, still shows that person, and the permission should name such uses explicitly. A synthetic model involves no real sitter, but the tool's terms on commercial use still apply. Requirements differ between countries and platforms, so the wording of each release is worth checking against the uses actually planned.