Maintenence is cheap... emergencies are not.
We have a client who cancelled their service contract with us to save a buck or two. It was made clear that we were not loosing them as a customer, just that they were cutting back on the routine maintenance which they didn't see a need for.
A few months later the inevitable happened... things started to break. We fixed it all of course (it was some sort of crunch time for the client, so they hit weekend rates), and then came the sticker shock. The bill was nearly twice what the maintenance contract would have been for the year, and the work would have been covered.
I didn't have to say "I told you so" since the client did that perfectly well. We did give them a 10% (discretionary) discount, but it still stung. On the other side, I have to admit that I am fine with the emergency calls. My bottom line hasn't looked this good in a year!