Dual Card Slots in my Olympus OM-D E-M1 MkII are very handy for back up during image making. Memory Cards can fail. Having Dual Card Slots in your camera is very crucial. Especially if you do wedding photography and venues that are one time things. You cannot re-make the wedding. With camera recording to two memory cards you have a back up straight away. The if you have a memory card failure your images are not gone. You still have the other one with the images.