If your website and proposition are able to drive good revenue via SEO, then there is a powerful chance that you can drive significantly more traffic and revenue from an intelligently managed PPC campaign.
One of the best aspects of PPC is that you can test your strategies very quickly and very cheaply and instantly and you can hone in on the optimum approach. Doing this also informs your SEO strategy about new opportunities, tells you which keywords are more fruitful and much more.
Organic traffic comes with its own risks such as Google penalties that shut numerous businesses in recent times. Having a second and extra source of new business makes perfect sense and finally, there is no alternative when you want to test an idea, take advantage of a short term opportunity, or level out revenue during a slow season.