Riding in a time trial position requires most riders to be 'on the rivet'. This can mean the rider has a forward rotated pelvis, with the sit bones typically up, off the saddle surface.
In this forward position, the pubic bone and other soft tissues become weight-bearing. Triathletes and time trialists tend to favour special saddles that have effectively had the nose chopped off, like the Fizik Tritone or a double-nosed saddle like the ISM range.
This also enables pro riders to push the saddle further forward on the rails, as there is a current (arguably outdated) UCI rule that limits how far forward the nose of the saddle can go.