Mostly companies rely on outbound marketing. Outbound marketing is a phenomenon in which companies reach out to customers by cold calling them, spamming them and etc. While inbound marketing is a phenomenon in which a company creates good content and people reach out to them. A total opposite of outbound marketing. There are other benefits to Inbound marketing is well. By creating good content you improve your organic/natural rankings in Google. Also, by applying basic SEO principles you can become a good Internet citizen.
However, there is more to inbound marketing. When people are searching for something on a search engine then normally they are directly looking for some information & there is even a good chance that they are a potential customer. So when they find your quality content odds of converting people (looking for information on search engines) into customer increases by an order of magnitude. Not only that, you get a lot of incoming links to your website & that helps immensely in terms of your search engine rank. More importantly, when you write good content you're considered as an authority and this surpasses every thing.
Just for the sake of example: as per Google almost 72,000 people are searching monthly on the keyword "Offshore QA". Now let's just suppose that out of those 72,000 only 2000 land to your website. Those 2000 see good content on your website and there is a good chance that they will refer it to their friends. Even if nothing happens we can assume that out of those 2000 probably 100 people will send us queries about our product. And if we can make 1 customer out of those 100 then in my humble opinion it's a big win. Because this customer was taken on board without any third party marketing services.
Putting good contents on your website improves your traffic a lot.