http://www.sencha.com/forum/showthread.php?329-createDelegate-...-huh
In JS, functions have no idea what object they are attached to and they don't care. The JS runtime generally manages setting the "this" reference in object methods for you automatically. In instances where you pass a function pointer, the "this" variable no longer is maintained for you automatically. createDelegate will bind a function to the correct object allowing you to pass a function pointer and have "this" continue to point to the correct object.