When you installed Zygor Guides Free Trial, quite a number of entry & files were created in the Windows Registry (What is Windows Registry) and hard drive, while running the default uninstaller always failed to remove all these data, it leaves us to manually track down and delete the leftovers inside the computer. This is an optional step, you can skip it and call it a day, but if you keep ignoring this every time you uninstall a program, your computer registry may become overloaded as such useless data accumulating, thus lead to system slowing down. Though it is optional, it is still recommended to do it as a good practice of using your computer.
I only subscribed about 2 days ago after coming back to WoW after 6 years. The game has changed so much since I left right around the Cata release. I decided to start fresh on a new server. I still had all my old links and logins to places like Curse, WowInterface, etc. Loaded up all the addons I had favorited years ago (of the maybe 1/3rd that were still maintained). Got to level 20 in a few hours of playing. Had to look a bunch of stuff up.