Probably more so worth it for portables: MacBook, MacBook Pro, or the MacBook Air just given the fact that they use mobile parts that are shrunken down and are subjected to being carried around, heat, and being confined in a smaller case.
I've sent in an older PowerBook G4 to have it's screen replaced, and fortunately AppleCare covered the cost. For non-accidental damage, AppleCare can easily pay for itself.
One might even make an argument to get AppleCare for desktops and monitors, but that's entirely up to the individual. In all likelihood, you'll never have to send in your computer to have it serviced. BTW, you have one year of coverage from the date of purchase of your machine. AppleCare simply extends that window of coverage to 3-years, but bear in mind, AppleCare must be purchased before the 1-year anniversary of the purchase of the machine. In any case, I could afford AppleCare and simply I'd rather have it and not need it than need it and not have it.