Laying hardwood on top saves time and money compared to removing the existing flooring and leveling it out. It makes the installation of click-in-place hardwood much easier.
Installing hardwood on top of laminate raises the height of the floor, which is problematic if it creates a tripping hazard or creates difficulty opening doors and cabinets.
Remove the laminate if it has holes, has caked-on debris or sticky substances, or is otherwise in bad condition. Covering issues like water damage or mold could worsen the problem.