This is my go-to example:

Say you want to make an autoloaded function in zsh. Go ahead and look that up. Unless you're one of the zsh maintainers, you probably don't have that syntax memorized. I don't mean that personally. The whole time I used zsh, I certainly didn't remember it and had to look it up each time.

In fish, you define a function named "foo" in a file in a specific directory: ~/.config/fish/functions/foo.fish. That's the entire process. When you type "foo" at the command line, and fish can't find that command anywhere, it'll look in that directory for foo.fish, and if it finds it, it'll load that file and execute the "foo" function defined inside it.

Now, say you want to customize your zsh prompt and have it show you the output of a couple of commands, maybe with some colors. It's a fun exercise to try to get something working purely from memory, but that's a test I never managed to pass.

Want to do it in fish? Follow that pattern above to define an autoloaded function called "fish_prompt". Put it in ~/.config/fish/functions/fish_prompt.fish. It's just a normal function where you can use "echo" and "git" and any other command on your system to write the components of your prompt to stdout. That's it. You're done. There's no step 2. Any other time I want to draw something on the screen, I'd use a series of shell commands to write it out to the screen, so why shouldn't it work exactly the same way for my shell prompt? Well, with fish, it does.

That expirement ruined bash and zsh for me. I don't spend a lot of time continually customizing my shell prompt, but the once every couple of years I want to, it's a huge relief to know I just have to edit that function to write out my new idea and that's the end of it. There's just so much less magic to learn and remember with fish that I don't want to go back.

And to be clear, I know my way around several other shells. I love fish because I've used the others enough to become very competent with them, not because I don't know the others or they're too hard for me or anything like that. By programming language analogy, I'm capable of writing decently sized programs in a few flavors of assembler. But man, life's too short to use it for everything, unless that's just the kind of hair shirt you're into wearing.

Bringing down my ZSH load times from ~3.1s to ~230ms