[Porsche-O-Phile]

Typically a restrained beam will because it cannot (as with a simply supported beam) distribute the load over the entire span via deflection. I'll have to dig out my structures books to verify with equations (it's been a while) but simply supported beams can deflect over the entire span whereas a restrained end beam must develop resistive moments at the ends and would deflect some distance along the span.

I'll double-check but that's what I recall offhand.