Allows you to toggle your quest tracker. Helpful if you don't always need to see it and need more space in your UI. Simply use the command /tqt or /ToggleQuestTracker to toggle your quest tracker.
If you're interested, I have also created an addon to toggle your minimap: https://mods.curse.com/addons/wow/toggle-mini-map and another one to sell your trash (gray) items automatically: https://mods.curse.com/addons/wow/selltrash