Right. It’s optional so that Bash remains backwards compatible as a superset of POSIX sh. If you’re working with exclusively Bash, though, it’s nice to use as syntactic sugar if nothing else.

Bash (specifically Bash, not POSIX sh) does have a keyword for functions (function), but it’s optional.

By some sheer coincidence, I searched this topic today. I’ve been a consistent user of the parenthesis expansion, but never thought of why I preferred one or the other.

I suppose the primary advantage is that $() will expand in a consistent way. You can even nest quotes and more expansions in one, while you’d struggle the same with backtick notation.

So I’ll just keep using parentheses.