Adjustable end link question
#2
Drifting
None unless your car isn't level and it causes a preload on one corner. Also, if you corner weight your car they are usually necessary to adjust the swaybars to not preload a corner. Ideally, there is no load (the bars do not apply any force) when sitting static. When corner weighting you typically adjust a corner of the car to be higher (or lower) to transfer weight which then requires that the end link length be changed to accommodate that adjustment.