One thing that troubles business including me is the fact that I have to bid for my own business name on AdWords and Bing. It drives people crazy. Why should I bid on Digital Firefly Marketing when I already rank number one? Why pay for the click?
The biggest reason people need to bid on their own name is relatively straight forward, your competitors can bid on it and when someone googles you they may end up with "those guys" instead of with you.
The second reason and actually the one that I found the most surprising is the paid traffic is actually additive to your organic traffic. In a number of studies, one done by Google and one done by NYU, people found the SEO traffic wasn't cannibalized for paid traffic but rather it was additive. There are a number of speculations as to why and some question of the data sets being too skewed to the U.S. However, I think it makes a great deal of sense in terms of not only brand awareness but simply giving someone more places to actually click. It may be just that simple.
Lastly, you will only know if you measure and track the analytics. How many leads came in from your PPC brand name v. your SEO name? What's the conversion rate? You may your brand name pays for itself in the long run.