Perhaps it's niche, but there's a single feature that makes me use zsh over bash: EXTENDED_GLOB, used together with * filename expansion.

    ls **/*.d

gives me all files, recursively, that end in .d. That's available in bash too if you `shopt -s starglob`.

But it also gives all directories, so if I do eg

    grep pattern **/*.d

then I get lots of error messages about trying to grep on directories (if I happen to have directories ending in .d). With zsh, I can do

    grep pattern **/*.d(.)

and it will restrict to just files. I use this pretty often, and it saves me from many `find | xargs` commands. I pretty much only use `find` when there are too many matches for a single command.

My muscle memory types

    fgrep -l SOMESTRING **/*(.)

multiple times per day. That'll list out all files containing the literal SOMESTRING anywhere in or below my current directory. I'm sure I could be using one of the fancy grep replacements, and I have in the past, but this works Good Enough and only requires zsh to be installed, so it's what I have held onto.