The problem with using shops is that you end up relying on them.
I recently paid for a Cyclesurgery ‘full service’ and in addition had some knackered parts replaced (cassette etc). On receiving the bike back I was initially happy to have paid for it – it almost felt new.
Two weeks later the snow comes, and my bike is knackered again. And to add salt to the wounds as I’m cleaning the bike my rear derauilier falls off. Nice. (Metal fatigue on the bolt that connects it with the frame hanger...)
So I was stranded in the middle of no-where (well, I was at home, but I don’t have a bike shop nearby or an easy way of transporting my bike to one). There’s more to the story, but essentially it just helped me decide that from now on – I’ll do it myself as that way I don't have to rely on anyone.