whilst stationary yes, just don't go driving round without it.
while sitting without panhard on flat level ground to further refine the position, I'd also measure distance from rim to rear arch lip (assuming they're not bashed on) and further tweak the rear axles lateral position relative to the chassis by tensioning with string or cable ties till both gaps are equal, then you measure the chassis bush - panhard bush distance and adjust the panhard length to match.