Filters can help enhance a photograph and make the scene look better. You could use a filter to change the way the camera captures the image or how the light is effective. Some filters such as a polarized lense can reduce glare and changing the hues.
Colored filters can be used to change to color theme of an image. If you add a blue filter it can make things seem darker as well as having a "wintery" or "cold" feel to it. Red could make things seem brighter while also having a "Angry" or a "romantic" theme.