The exb-m256 will allow you to use all the extra free PCM piano and orchestra sounds korg gave us at the same time and use more of your own samples. Without the M256 only one of the PCM sounds bank for korg can be loaded at a time. You have to load them up every time you turn on and off your M3. The PCM sounds can be setup up to load automatically(not instantly) when you turn on the Korg M3. Your samples you will have to go in and load. If you do not desire to use your own samples nor do you want to load PCM piano and orchestra sounds Korg gave us for free then there is no need for this expansion. I still recommend you get the expansion anyway. It adds value and you never know when the extra ram will be need in the future.
