I use them on sidings so that I can drop off and pick up cars.... As "sinclair" noted.. placing one too close to a switch will cause an accident, also keep in mind that immediately next to curve piece of track can be a problem too... when you are dropping a car off with the uncoupler, the coupler you open on the freight car your leaving behind will be sitting right over the magnet.
When you come back in to hook up the couplers through a curve section of track after the switch, the couplers may not line up and engage each other, this problem gets more severe with sharper curves. Best to have some cars handy when you're laying the track, open the coupler park it on the siding and see if when you roll the next car in, the couplers line up.... Hope that helps.
