Yes. Unless you don't want your channel on older devices, I think the 4.1 firmware and later just uses the mm_icon_focus_hd and sd images and ignores the side image, but if you care about getting your channel onto 3.1 firmware devices, then you will create HD and SD side focus images (SD images, both focus and side, should be NTSC SD aspect ratio when created)
The reason to use different images is that the side and focus images are different dimensions, channel artwork will look squished if you don't take the time to make an image of the correct size for the side image.
- Joel