Provides a better seal and allows you to pump out the bean hopper, as the lid is deep and has seals.
Thus by grabbing the lid and pumping up and down, you can flush all the ground coffee out and much easer that using a brush..
Got to fine one that suits the SB EM0480 as well.
PS. Kmart have them... The contained can then have the Rocky lid fitted and you still have a something useful.