Ok I see. So it would be useful to people who want to implement deferred lighting with SFML... which seems too specific to me.
From the point of view of a regular user, this class would be useless, nobody would be able to get something interesting from it.
SFML doesn't aim at providing a complete OpenGL wrapper, but rather a simple and consistent API for 2D graphics. For this kind of advanced/fancy stuff, you'd better use OpenGL directly.
I hope that you understand my point of view