The basic setup loads SLIME always, even if you don't use SLIME. Emacs will start up a little faster if we load SLIME only on demand. To achieve that, you have to change your ~/.emacs slightly:
(setq inferior-lisp-program "the path to your Lisp system")
(add-to-list 'load-path "the path of your slime directory")
(require 'slime-autoloads)
(slime-setup)
The only difference compared to the basic setup is the line
(require 'slime-autoloads). It tells Emacs that the rest of
SLIME should be loaded automatically when one of the commands
M-x slime or M-x slime-connect is executed the first time.