In most cases there is no real need to use filters these days, but, one exception is a polarising filter (and ND grads...!)

The polariser (Nikon 77mm above) is the one enhancement that does things to an image that cannot be recovered in Photoshop later. The photos were taken 6 seconds apart.

Move your mouse over the image above to see the flare dissappear and the colours enhanced... I mean just try painting in under the sun spots!