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.
Besides registry cleaner, it is also necessary to perform a defrag for your computer hard drive regularly, which is not only a good way to optimize your computer system's structure, but also can help you clean those fragments created in the incomplete program removal. There is a specific computer defrag utility available on the Windows operating system that enables the computer user to perform a defrag for the computer disk, or you can choose a free third party defrag tool like Auslogics Disk Defrag that opimize your computer disk in a quicker and more effective way.