Just to expand a little bit. Go Launcher is just another app that runs on your phone and lets you replace the App Launcher in it, and to do so it doesn't require any 'special' permissions since Android is designed to let you do just that: Customize your system.
However, there are a few things that require more permissions, like tinkering with your notifications, accessing hardware in a low level, writing/reading files in the protected section of your phone (this is where rooting gets dangerous). To access all these, you need to 'root' your phone, or gain write/read access to the protected section of your phone. This gives you access to EVERYTHING in your equipment and, if used properly, lets you do fun stuff you couldn't do otherwise, but it also means that these files (some critical to your phone's functions and, if broken, may permanently damage your headset) are wide open, so privacy and security are VERY MUCH lowered.
It's sort of like Jailbreaking an iDevice. It lets you change things you wouldn't normally be able to change, but it also leaves your phone open to malicious attacks or to just an installation/overwritting mistake that could render your phone unusable.