I think complexity is really down to their needs and what they like or want, if they have a creative idea and put that idea to a good designer it can turn out awesome. I think a lot of it is just creativity and thinking outside the box and trying something different whilst maintaining professionalism and they end up with a really good looking background. It also helps if they can design one for themselves, it can be cheaper if they already have editing software but it can be a learning curve if they want something that looks awesome.