Not just the next parenthesis that appears, It jumps to the matching one that opens or closes the one under the cursor. Hitting it repeatedly bounces back and forth around the text that pair of parentheses enclose.

It works not only with brackets and curly braces, but also with opening and closing tags in XML etc.

I feel like other editors must have an equivalent feature, though. I'd say the fact that vi can put such a specific action under just % rather than some nasty chord or mouse operation is what really makes it shine here.