Also, with VM, you don't have to wonder if the guy is at his desk/near a phone/busy with somebody else. I loved it, partly for the reasons Milt mentioned. Avoid time wasters. Put in the information the receipient needs in order to act upon your message. Don't you dare VM someone to say "Give me a call". Let them know what you need, so they can actually have the information when they do respond.
My boss, co-workers & I were spread out over a couple of hundred miles, sometimes in with clients, sometimes between locations. You soon found out who were trustworthy with the system and who needed a copy of the message sent to his boss.
Les