The Theme Design Utilities plugin offers a range of helpful tools for Obsidian theme designers. It includes features like mobile emulation for previewing themes on mobile devices and the ability to cycle through installed themes or toggle between light and dark modes. The plugin also provides commands for debugging, such as adding red outlines to elements or freezing Obsidian for creating test elements. Additionally, it offers helpful resources like cheatsheets and markdown notes for testing theme colors and CSS adjustments. These utilities streamline the theme design process and improve efficiency within the Obsidian environment.