For those still making single-player HL2 maps (if there are any : ), I've posted an example map illustrating the use of assault entities.
FYI:Assault entities are used to initially position NPCs and then move them to assault positions on trigger. They're used extensively in the HL2 coast sequence to launch combine assaults (as Freeman approaches Nova Prospekt along the coast, turns off the thumpers and he and his troop of antlions take out the bunkers).