This is a prime question that needs answering. Most clients already aren’t that familiar with graphic design when they come searching for services. They may also be looking for a specific service, so this is an easy place to spell out exactly what you do. It also allows you to showcase your expertise and ensure that you don’t waste time on leads that don’t actually want the services that your firm offers.
You can list things here so that they’re easy to find; take it one step further, too, when you link to service pages or other areas of your website to tie everything together. Sure, you do have that list of services or service pages on your website—isn’t that enough? Unfortunately, it’s not. People want easy answers so they’re coming to your FAQ first and if they can’t find it there, they might not bother looking elsewhere.