Look at the bandwidth requirements for the various speeds. At higher speeds the physical characteristics of the cable are very important. You need a specific number of twists per foot and the overall diameter of the cable is important. If Godzilla hangs off the end of the cable, these cable characteristics will be distorted and the top speed capability will tank.

On occasion I'm brought in after the "smart" carpenter has had his apprentice pull all the networking. While the wire seems to go from here to there and the wire map is OK, there can be wire nut splices and areas that are stripped bare, with conductors shorting to pipes and metal studs. I've also seen daisy chain networking.