I love keyboards. By saying that I love keyboards, what I'm also implying is that I don't really like using a mouse. So, anytime that I can accomplish something without the mouse, I'm all for it. GPMC.MSC is a tool that can be used in a myriad of ways. It's not really a tool per se, but rather an MMC shortcut. When you launch GPMC.MSC, it opens the MMC and automatically snaps in Group Policy Management. In other words, by issuing a GPMC.MSC command, you are shortcutting your way into the GPMC.
GPMC.MSC can be launched from just about anywhere that you can type it. Certainly, the most common place I type it is inside either a Command Prompt or PowerShell prompt, since I almost always have one or the other open all the time: