There are many ways to reach an audience. Most people focus on paying money to reach somebody else's audience via advertising on such platforms as TV and radio, search engines, trade show exhibit floors, and so on. Another way is to build your own audience by creating content on your site or via social networks.
Both approaches can work, and both are strategies that can be part of a marketing plan.
However, I like to think of advertising as like leasing a car or renting a house. You pay every month but when you're at the end of the term you have nothing. In other words, when you stop advertising, you are not building new awareness.
With content creation, every month's investment builds an asset that is yours that you own forever. Blog posts from a decade ago can still drive traffic to your site.