Every laminate manufacturer we install lists a flatness tolerance in the warranty. The common number is 3/16 inch over 10 feet, and some lines ask for 1/8 inch over 6 feet. Skip that step and the warranty is gone.
Why it matters: a click-lock floor floats. When a plank sits over a dip, it flexes every time someone steps on it. That flex wears the locking profile, then the joint opens or clicks under your feet.
We check the whole area with a 6 or 10 foot straightedge. On plywood and OSB, we screw down loose panels, plane or sand high seams and fill low spots with a floor patch. On concrete, we grind ridges and use a trowel patch or a pour of self-leveling compound for bigger low areas.
Leveling adds time, sometimes a drying day, and we put it in the written estimate so it is not a surprise. It is the part of the job you never see and the reason the floor feels solid ten years later. Leveling is standard on most laminate over concrete jobs.