wossupdog, don't let the terminology confuse you, a semi-rigid or rigid rotor system simply lacks some or all mechanical hinges; the blade must still flap, drag and twist but the rotor head is made of materials that deform sufficiently to allow this. For example on a Lynx (semi rigid with about 17% effective hinge offset) the feathering is permitted by a mechanical sleeve and bearing and flapping and dragging are permitted by bending of the titanium rotor head and the blade root respectively. The blades still flap to equality but the movement of the blades is controlled by the materials of the rotor head and not hinges.
The main advantages of semi rigid/rigid heads are ease of manufacture/maintenance and control power; control power can be defined as how much the fuselage responds to a given control input ie snappier pitch and roll response. The blades act as a lever on the fuselage and they force it to follow their flapping - the bigger the lever the faster the fuselage response to a control input. This is what the percentage of effective hinge offset indicates - the higher the percentage the faster the response.