Canon 5D cameras can use SD and CF cards simultaneously. I personally use the "less professional" 6D, which is SD-card only, but even for the "more professional

Canon 5D cameras can use SD and CF cards simultaneously. I personally use the "less professional" 6D, which is SD-card only, but even for the "more professional" 5D users, it makes sense to me that they might want to load JPEGs off an SD card onto their laptop for quick editing, and RAW images off a CF card onto their Mac Pro. [EDIT: though, of course, if you're already hauling around a laptop and an SLR camera system, it's no big deal to keep an external card reader in your bag too...]