If the sun is at you back and there are no strong light sources near the edges of the image area a lens shade is not essential, but in high flare conditions a lens shade is a good idea. You will see flare in the dark areas of the image and color saturation will be adversely affected. Its a good idea to keep direct light off the lens whether using a polarizer or not. If you don’t have a lens shade you or a helper can cast shadow over the lens with a hat or anything just keep it out of the picture. If you look at pictures shot in a light tent there is often flare and the blacks in the image are milky and the color saturation is down unless the lens is carefully shaded.