Shock troops receive higher close combat value in exchange for higher casualties. The shock bonus is rare in CAOS and as of Beta version 2.9.2 ALL Russian Guards formations and German SS formations receive the shock bonus.
It is worth noting that the shock bonus is applied to units during combat resolution and may not apply to all combat orders. For instance an SS unit may benefit from the shock bonus while conducting any king of offensive combat order but not while reserving another friendly unit.