As I asked here, I couldn't make it run Aquamacs/slime/clojure, but I could use Auqamacs/clojure with 'M-x conjure-mode', then C-c C-z (run clojure) and C-c C-e (run expression).
I don't have an experience with SLIME, but I feel that C-c C-z and C-c C-e is just enough for lisp/conjure REPL or debugging.
What features SLIME has more than these features? What people use SLIME for?
So, so, so much more.
M-. to go to a definition.
C-c C-k to compile the current buffer.
M-p & M-n to go forwards and backward in REPL history.
M-<tab> for completion.
A debugger. A wonderful REPL.
And so much more.
Slime gives so much: look at its manual.
It shouldn't be too hard to set up: this post is a great starting point.