What is a color wheel
A circle shape that is divided equally in to 12 sections, with each section displaying a different color according to its pigment value. As all colors are created from the three primary colors (red, green and blue), the primary colors are shown forming a triangle within the color wheel. The color wheel shows the relationship between the primary colors, secondary colors, and complementary colors.
I’ve seen photographers say you should get a color wheel and understand the relationship between the primary colors and the secondary, and complementary colors.
The color wheel is designed for decorators to coordinate colors as they are putting together fabrics, paints, wall papers, etc. and make sure all the colors work together.
I don’t see how the color wheel has any value for a photographer because we don’t get to choose the colors that are in our subjects, the subject colors are already determined and we shoot what is there. If it’s a great subject, I’m gonna shoot it regardless if the colors work on a color wheel, so again not sure why photographers talk about the need to learn the colors of a color wheel, because we have no control over the subject color. Unless you want to change it in photoshop.
Mike Moats 
Mike, I have to take a different tact on this subject. I think having a sense of color relationships helps us to see and pre-visualize what scenes in color work best. It also helps during the post processing processing. I think there are many fine resources on the subject and it is subject that has interested for a long time. You aren’t going to change my mind, because it is an important part of seeing and understanding what colors tell a story best.
Not all photographers shoot landscape or “existing” scenes or elements; many create scenes, shoot models, introduce elements into a scene, etc. And a knowledge of color is important and valuable in those situations when choosing wardrobe for example or which color bowl would look best with certain fruit. And, all knowledge is good.
Where I use the color wheel is in post processing. If I find I have captured opposing colors I can then use the HSL adjustors in Lightroom or in Impression or Glow to bring them out. They aren’t always present in the natural setting, but if they are there inhancing them in post really can cause the image to pop.
Composing the image often means I change my angle to to get a distracting color out of my image. It can also mean I quickly arrange a shot so that it will include the color relationship I see when a butterfly lands on a specific color that is pleasing. Maybe you do not have to learn the color wheel to use it, but I think you may instinctively choose well.
Mike, there is one area where I would disagree. In our long cold winters, I often buy flowers to photograph indoors. I often make my choice based on colour and what I expect to do with the images.