UI Themes is a tool for customizing the appearance of widgets and centralized customization management (works with UGUI).
It allows you to control and change colors, textures, and fonts from one place.
It is useful even if you do not have plans to use different themes.
For example, you have a couple dozen prefabs and want to adjust colors or replace sprites. It can be an annoying task to change settings for each of them and be sure you do not miss anything. The theme helps you to avoid such problems.
Easy to integrate and use with already existing UI.