The lead/lag adjustment on a two-bladed helicopter is for assuring the rotor system can be balanced (180 degrees apart, nominally). Otherwise, the resulting imbalance, will drive you crazy, and wear out parts prematurely, and can be dangerous.
Visualize a string pulled taught from the outboard tip of one blade, through the "center" of the rotor shaft and pulled to the outboard end of the other blade. If the blades are too far to one side of that string or the other (not 180 degrees apart), an imbalance will occur. Further, there needs to be an adjustment mechanism because it's not only the geometric requirement of the two blades needing to be 180 degrees apart (nominally), but very small changes in weight of one blade or the other, will affect the this balance, such as uneven paint wear on the end of a blade vs the other.
A fully articulated rotor hub (three blades or more) is vastly more complex. If the imbalance described above occurs on a fully articulated hub the whole ship can self destruct in a matter of seconds. Do a Google search on "helicopter ground resonance".
With gyrocopters... we take the blades apart when we trailer to a 'gathering' (fly-in).
When one puts the blades back together (attach each blade to the hub)... we always 'string' them... similar to above.
This is very critical... otherwise there will be vibrations enough to tear something apart...
And we now one cannot 'park it on a cloud' and fix it.