There are many advantages relative to bash, especially much better array handling, and comprehensive globbing and expansion expressions. You can reduce your reliance on external tools, which may have multiple alternative implementations (a source of unpredictability).

Some defenses are written up at

https://www.arp242.net/why-zsh.html

(not my post)

For me, fish’s differences from older shells count against it without offering any compelling benefits.

Newer shells like nushell and oils/ysh are exciting and have a lot going on, but are not mature or familiar.