Leave the designing to the designers
You always want to put your best foot forward when presenting to clients. You want the materials you distribute to be just as professional and polished as your sales pitch. Although it may be tempting to create your own marketing flyers to save money, graphic designers have the knowledge and creative eye that is worth paying for.
Resist the urge to open Microsoft Word and start designing your own materials with generic clip art, crazy fonts, and colors that don't complement each other. Microsoft Word in far inferior to the capabilities of the design software graphic designers use to create documents. Not to mention, most freelance graphic designers offer reasonable rates for their services.
A good graphic designer will help you organize your message into visually appealing and effective marketing collateral. Graphic designers don't just make things pretty, they make your company look professional and polished on paper, the web, in emails or whatever other medium you may use to market to clients.