It is particularly important if you are serious about photography because if you labor over a given photographic creation and then your audience doesn't see it the way you intended it to be seen, your message gets lost. So much of what a photograph conveys is in the subtle colors and shades... you can change the whole mood and meaning of a photo by getting this stuff messed up.
That is why I recommend going out and getting a roughly $100 hardware calibration package if you are serious. At least you know that YOU are seeing the right stuff as you work on your creations. As to the person viewing it... well, if they are serious, they will have done the same. For stuff you are publishing on the web, you can adjust your colors for the more or less standard web color space, sRGB, and know that most people will see the result *very nearly* like you intended!