This essentially will push your date out further so it's not something you'd use often, if at all, if I understand it correctly.
In the OP's case he got it done at another dealership so he reset it to keep track of when the next one should be. But in my case for example, I recently did a non-scheduled oil change and told them NOT to reset the pc, thus enabling me to get my scheduled one later for "free."
Sorry if what I'm saying is obvious :P
335i E90 / Arctic / Gray / Burl Walnut / Steptronic / ZPP / ZSP / Paddles / CA / Nav / PDC / OEM Spoiler
Mods: PIAA Angel Eyes, Rear Fog Switch, Escort X50 Blue hardwire, 30% Charcoal Llumar
Installing soon: Rear Power Outlets (Happy Robot mod!)