Well it just adjusts the time the shutter stays open (and/or sometimes the aperture size), which lets much more light hit the film, well sensors. It'll give you more brightness and better colour, you can over-do it though. Have an experiment on the same sunset with Minimum, then Maximum exposure and see the difference.
Oh Also, have you ever thought about taking a panoramic picture of the sunset? If you take lots of photographs at a different angle each time, you can paste them all together in an image editor and get a really wide, impressive picture.