please explain why evil-leader is better than a custom keymap

[wbolster]

please make it more clear why evil-leader is useful (either in this issue, but preferably in the readme).

for instance, this also seems to work fine to get some basic "leader key" behaviour:

(defvar my-leader-map
  (make-sparse-keymap)
  "Keymap for 'leader key' shortcuts.")
(evil-define-key 'normal global-map "," my-leader-map)
(define-key my-leader-map " " 'whitespace-cleanup)
(define-key my-leader-map "b" 'list-buffers)

clearly i'm missing something. please enlighten me. :)