Maybe I ate some paint off the wall in the 70s ( "Lead paint" Get it? 
) but I still don't understand "You can also cause all additional macro instances to be immediately cancelled by setting a very short timeout (1 hundredth of a second) for the Semaphore Lock Action. When the Semaphore Local Action times out, it cancels the pending execution of that macro instance."
Can you perhaps give an example of why would it be desired to cancel all additional instances? Sorry but I've read it about five times and still don't get why would this be necessary/desired.