Minor weakpoints are points in buildings that disable the structure, much like killing it would, albeit without actually doing so. In exchange, there are repair nodes throughout both Allied and Soviet buildings that will let you repair just as fast as if you were repairing at an MCT, but not have the MCT's weakness to damage. That damage bonus goes for the major weak point, and if I'm wrong on any points, may the devs feel free to correct me on it.