As a business owner, your ultimate goal is to have a website that attracts passing by (virtually) clients organically without spending a lot on any paid advertisement or ideally no paid advertisements (which is the goal). Optimizing the content of you website with right keywords is a great method of generating leads for you for years to come without spending any further dollars on advertisement. Plus you can work on this advertisement from anywhere in the world as long as you have a computer and internet. You don't need to meet clients face to face which saves you a lot of time and money. Other advertisement methods are still useful and highly depend on your industry however with the growing trend of online shoppers using Google as their main search platform for shopping their products and services, a good website with content optimized for the right keywords is very important.
When your website is new, in the beginning, you might have to use some paid advertisement to get more traffic to your website. This will also help google algorithms too. Gradually you can move from paid to organic as the ultimate goal is getting a fully organic traffic.