Android Studio: What does the blueprint area do? What benefit is it?

AFAIK there really isn't any 'huge' advantage to the blueprint view. It provides a wireframe view of your design.

There are a few cases where it comes in useful though, for example,

• If your View is invisible, it won't be seen in the preview but it will visible in the blueprint view.
• Overlapping views are more clearly visible and identifiable.
• It provides a more clutter-free view where the constraints and views are more immediately identifiable.
• It's also used to be useful for preview of components that are 'invisible' (for example, imageview who's src get set programmatically).
• Rendering the blueprint view is faster. (As pointed out by Martin Marconcini in the comments)