One of my the filters I use most often while shooting outdoors is the circular polarizing filter. This filter acts very much like a putting a pair of sunglasses on your lens. It serves to cut reflections, saturate colors and add contrast to a picture. With a circular polarizing filter, you can control the degree of polarization by rotating the outer ring of the filter--and just dial in the amount of the effect that you desire.
While visiting the Wisconsin Capitol building in Madison, I noticed a contemporary building with all glass walls. Out of habit, the first thing I did was to reach into my bag for my circular polarizing filter. This is the first image that I captured. Note how the filter has eliminated most of the reflections from the glass--which allows the colors to deepen:
Here's how the image appears without the filter:
Without the filter, the reflections are more pronounced and much of the color from behind the glass is removed.
Both images are acceptable and some viewers will prefer the first version while other viewers prefer the second version. However, I was envisioning a different shot that would not utilize the filter: