A polarizer reduces the amount of light that enters your lens. If you need to shoot fast, like in a dark canyon or a night time rock concert, ditch the polarizer. Low light situations won't benefit from a polarizer because you'll need all the light you can get for fast shooting.

Should I always use a polarizing filter?

Using a polarizer in landscape photography is often advised. And with reason: colors will be enhanced, reflections in water and on the leaves can be removed, and skies can turn deep blue. But it is not advisable to use a polarizer as a standard filter, because there are situations when it can turn against you.

When should you not use a CPL?

It's generally not a good idea to use a circular polarizing filter with a wide-angle lens. This is because CPL filters work best when they're at a 90-degree angle away from a light source, such as the sun, and a wide-angle lens usually covers more than 90 degrees.