Three main types of WiFi site surveys exist:
Unless the router is so powerful that it can provide sufficient coverage despite poor placement (something not many home routers can do), its less-than-optimal place of installation results in the so-called dead zones, which are areas of signal weakness that can cause slowdowns and connection drops.
The real culprit is almost always poor WiFi coverage caused by the fact that most people place their router near the closest unused electrical outlet, sometimes hiding it away from view behind a piece of furniture. WiFi issues are one of the most common problems Mac users experience, and their computers are seldom to blame.
