Graphic design is a necessity for any business. A business needs a logo, business cards, website, marketing material, flyers, posters, signs, menus, etc... We do that, plain and simple.
Some companies like to try and create logos and other marketing materials on their own without the knowledge of a professional. This works out for some, but for most it ends in disaster and costs more in the long run. You have to understand pixels, scaling, raster vs vector, colors, printing and more. Those are just basic items and there is much more to good design but without the baseline knowledge of those key topics, a non-professional design could end up being a disaster down the road.