I very strongly disagree that you need or even want OMZ. You don't need it for Bash, why would you need it for Zsh?
It might be nice when you're getting started, so you don't have to learn all the ins and outs of the shell to have cool prompts and other useful functionality.
It might be nice when you're getting started, so you don't have to learn all the ins and outs of the shell to have cool prompts and other useful functionality.