There are metal roofing panels that simply overlap on the vertical and/or horizontal seams, and metal roofing panels that actually interlock wherever they connect. There are obvious benefits to fully interlocking panels. Those benefits typically include increased wind resistance and less chance of weather infiltrating the roof system. Over time, with overlapping panels, ice, snow, and debris from trees can work its way between the overlapped panels, forcing the overlap open. This just invites more debris and leads to compromise of the roof system. Overlapping metal roof panels also often have exposed fasteners and those can be points of entry for rain water as well.