1. No need to mess with configs. Works out of the box.

2. Breaking Bourne Shell compatibility. Personally I find Bourne syntax hard to learn and hard to read. Fish syntax is much better. [1, 2]

[1]: http://en.wikipedia.org/wiki/Friendly_interactive_shell

[2]: http://ridiculousfish.com/shell/user_doc/html/index.html

Sounds like there's no reason for me to switch.

I've already messed with configs and everything is stable now, so that's a sunk cost.

I already know bourne-style syntax, so learning fish (even if it's easier) is an added cost, not to mention the fact that I have to work on various boxes that I can't install fish on so it's easier to have my fingers know how to operate a single shell (zsh) that's generally backwards-compatible with bash (which is ubiquitous).

Funny I was about to say the same thing about installing on systems. When you're a systems person or work with many different customers you can't ask them to install a custom shell. Try explaining to the CIO at a major bank why all his linux boxes need fish shell installed.

So we get stuck back at the minimal set of SH syntax that I learned to master some 25 years ago.