So, I've never thought about it before but I've always traced lines without unpluging them from the switch (cause the reason I'm tracing them is cause I don't know which one it is.)
I've never had a problem with this and I know other people who do this. However I did this to day at a location.. and it stopped ALL network traffic at that site.
The only difference is that I usually work with Cisco solely, these I haven't gotten to upgrade yet and there still netgear (managed layer 2 switches)