“One picture is worth a thousand words.” 
– Albert Einstein

In the early 1970s, when I started in the design business, illustrations were one of the major tools used to get an advertiser's message across. Once the digital age arrived, and the cost of using full-colour photography in print dropped (and Photoshop made the task of retouching and manipulating photos more common) the use of illustrations reduced. Although producing illustrations is no longer the biggest part of my business I have seen a bit of an increase in demand over recent years.

Here are a few examples. Unfortunately I cannot show images that were done for other designers or advertising agencies, but these may give you some ideas for styles of illustrations that may fit into your marketing campaign.
Click on any image to see a larger view.