Bash is the de facto standard for shells. On Mac you are equipped with zsh which is a superset of bash. You don't need to be an expert, but you need to learn it.
Why is it useful?
- A lot of times this is the only interface you will get when you are working with remote systems
- You can automate good chunks of your repeatable tasks
- You can manage processes and environments faster
- New features come first to the command line interface
You will know that you are good enough (for now :)) with bash when you have automated via aliases, cronjobs or a script at least one common task you are currently doing.