I'm not sure to be honest, I've been working with Clojure for 5 years now, and the only "help" I get from the editor I get is "highlight matching pair". I never got used to automatic paren insertion or things like paredit.
The following are all a single key combination in most editors that support Paredit or equivalents:
- Kill an entire loop or data structure to the right of the cursor
- Swap two deeply nested expressions to the left and right of the cursor
- Absorb ("slurp") or expel ("barf") expressions to either side of your current expression, into that expression
- Delete the entirety of the expression enclosing where your cursor is, leaving everything to the right intact but raised to the enclosing level (this one is amazingly common but you would never think to use it until someone shows it to you, after which you use it every day)
It takes a couple of days to get these and many other shortcuts into your fingers, after which it's hard to live without them. http://emacsrocks.com/e14.html is a good introduction.
Structural editing is the first thing I miss going back to Python, Ruby, JavaScript, etc. That, and, of course, instant REPL evaluation of the expression under my cursor.