Linux

Not to say this is gospel truth or anything. It's just why I virtually always prefer a command line over a GUI. (Within reason.)

• GUIs almost always hides/obfuscates/abstracts things that are going on under the hood in a way that text doesn't.
• Anything I can do from a Bash terminal, I can automate pretty trivially. (Or even just press "up" and then "enter" to quickly redo it a second time.)
• Pointing devices feel awkward and imprecise for a lot of operations. Pretty great for FPSs. Sometimes a necessary evil for image editing. Slow and sucky for setting a boolean value or putting your text cursor between two specific characters in a paragraph of text.
• It's good to be able to use a terminal when your GUI's broken or frozen. Ctrl+alt+f2 or if even that doesn't work, ssh in from another box (or your phone).
• It's a lot easier to paste a Bash one-liner into a chat or text file than describe a series of mouse clicks.
• You learn a lot using Bash that you don't learn using GUIs. And that can come in handy.