Helicopter Basics: How does lead-lag of blades actually help in compensating for increase/decrease in speed due to flapping?
Blade flapping is simply the action of the tilting of the rotor disc; the blade's tip is following a particular path attached to a hub that is rigidly fixed on its vertical axis. The blade flaps up and down because its incidence/pitch is being continuously varied (or not if the stick is centered) by the swash plate.  The limits of the rotor disc's tilt range is, beyond the swash plate limits, ultimately the blade flapping travel limits.  Articulating rotors can handle this, but on a two blade teetering rotor, achieving those limits is called "Mast Bumping" and is a fatal condition.

For lead lag, the issue is you need to allow for that motion on an articulating rotor helicopter because Coriolis force makes a blade want to speed up as it flaps up relative to the other blades (actually, moving off perpendicular to the mast's axis).  When it flaps up, its center of mass moves closer to the hub than a blade on the other side that is closer to perpendicular to the mast, which makes it want to speed up, like a figure skater pulling arms in while spinning.  The lead/lag hinge provides the necessary compliance to accommodate the speeding up and slowing down tendency of the blade as its center of mass moves closer and farther from the mast as it rotates while moving up and down, so it doesn't force the rotor hub to absorb the forces.  The lead/lag damper is there to resist sudden movements of this lead/lag action that can be caused by sharp ground contact, which can lead to ground resonance.

On a teetering rotor system, you don't need lead lag hinges because you have the geometry of the teetering hinge, which is the blade flapping hinge for both blades on a single flapping axis.  The up flapping blade moves away from the hub because the hinge is above the blade axis (called an under slung hub) and this keeps the CG from moving closer to the hub significantly, eliminating most of the Coriolis forces, or reducing them to a level can be absorbed by the rotor head and blades.