I get the idea that from a center point of reference like the center of the lens of a projector, the edges of the screen will be a longer distance than the center point directly in front of the lens. That's basic geometry and algebra. I get the idea that by *slightly* curving the edges toward the lens, you can maintain the distance from the lens across the entire screen, improving focus. However, with today's modern digital projectors and lenses, I would think that the only noticeable difference would be on extremely large screens, not something you would use in home use.
Just a SWAG.