In my opinion they make a huge difference in the final outcome of a project.when you spend a little more on material ,you tend to save more on labor. Which in most cases is more expensive. When you install quality materials you usually end up with a superior product.and in a business sence you earn a better reputation which in turn brings you more clientele which makes your business grow and become more profitable.
Quality is better than cheap. So many time I meet owners that want me to use the cheapest materials , but make sure it looks good. Reality check the paint at Wallmart is junk, but if you use Benjamin Moore, Berh Marquis, there will be a great difference. And satisfaction to boot.