JCA34F:
Have you ever tried putting one Fluke probe on the "hot wire" and probing the circuit with the other?
Once in while, some time ago I did it when in tight spot, I kept other test prope badly and somehow touched it... while another one was still on live. it still hurts bit too much even it go thru fluke. 
Dont think that current would be more than some mA or even bit less. but when you are inside relay logic case, you dont want anything extra
Also apart to get stronger current sink when cutting 0 (was mentioned before) , its also easier just cut 0 when playing with npn transistor switches. no need to worry voltage that is cutted (ok, can be done also with pnp to cut 12V, but you need to be sure about that voltage.