Gradient maps are a powerful tool in Photoshop and when utilized correctly, make for a quick and easy way to effectively tone your images. Travel Photographer and Videographer Travis Transient has a quick tutorial on how to best utilize gradient maps to color grade your images.
A gradient map evaluates the highlights, midtones, and shadows in your image and "maps" them to various colors as determined by how you define the gradient map either with presets or by creating your own. When you first apply these to your image, it will more than likely give you a suboptimal result. The key is using the opacity slider to subtly tone your image with the underlying colors in the gradient map. Understanding the various blend modes and applying the right one to your image can also make a big difference.
A common cinematic color grade is the orange and teal look with orange added to the highlights and midtones and teal (a shade of blue) added to the shadows. Orange and teal are complementary colors and thus, go well together. This look gives your image a pleasing golden hour feel to it and can be easily achieved using a gradient map.
You can also use gradient maps to create a custom Look Up Table (LUT) which can be applied to video footage as a base color grade. What are your go to gradient map color combinations? Anyone creating their own LUTs?