In the old days of film photography, photographers often carried around a handful of filters. Because white balance was baked into the film, one would often have to correct for various light sources using filters. The film itself was balance for the yellowy warm indoor lighting or the cool bright white of sunlight. Going from indoors to outside or visa verse required changing film or adding a filter to your lens to cool or warm the light.
Black and white photographers would use colored filters to effect certain color ranges. For example a red filter would be used to make some serious tonal changes: pink and orange go almost white while the deep red displays similar values to the original orange. While the blue and green become very dark.
In the age of digital photography, white balance is not longer a worry and can be changed in post production if you are shooting RAW files. Other filter effects can be achieve using software such as Adobe Lightroom, Photoshop or OnOne Perfect Effects.
A polarizing filter is used to cut glare off windows or water just like a pair of polarized sunglasses. A UV filter doesn’t do anything in the digital age except add a layer of protection to your lens.
A polarizing filter can increase color saturation in landscapes it removes glare off leaves. A circular one allows you to dial in the right effect.
A UV filter can be used all the time. A polarizing filter should not as it takes away one stop or so of light. Also in wide angle shots you can get an uneven effect across the sky.
Just bring out the polarizing filter when you need it to cut glare.
Other Useful Filters for Digital Photography
Here are some other filters you’ll find useful for digital photography:
Graduated filters – If the sky is too bright you can use a graduated filter to darken the sky.
Neutral Density or ND filters – Neutral Density filters darken the scene without changing the light. You can get them in various strengths or get a circular one that can dial in the intensity. Why would you want to darken a scene? The primary reason is to be able to use longer exposures for smoothing out waterfalls to get that silky water look.