From what I've seen, "call parking" is more common and far easier to understand than call transfers on office phone systems. As long as the volume of transferred calls is small enough never to overflow the one or two "parked call" buttons, it's much easier to just park a call, call the forwarding extension, then explain that so-and-so is waiting on Park 1. This also has the advantage of allowing the forwarding party to pick up again if there is no answer, and for the call to wait a few seconds until the new recipient is ready. To see how much more intuitive it is, try drawing a diagram of call forwarding without using an extra location for the call that waits in limbo to be transferred.
Mokalus of Borg
PS - In case you're not familiar, "parked" calls are just on hold.
PPS - And anyone can pick up.