In almost every bag you will find a polarizer and on almost every lens, a UV haze or clear filter. Your polarizer because it does things you just can't do later in a saving you Red Bull and carpel tunnel in the late nights. Simple Ultraviolet (UV) fliters are there to protect your oh so expensive glass from the elements.
Filters are like a child star that used to be big. Somewhere along the line, the industry just lost interest. In the new digital age, most special "filter effects" are applied in post production. There are however, a couple of filters that survived the career slump that the rest of their brothers fell into.