According to statistics, the first result in a Google search gets 24-40% of the clicks. Top 5 results allocate over 80% of the clicks. We see similar figures also for other search engines.
Obviously, if you are among the top 5 for a search, you will attract many more potential customers. This is a simple example of what SEO can do for your business.
In any relevant search your website works as an advertising for you. You do not pay for the number of "impressions".
Unlike TV commercials and billboards, SEO optimization helps to reach people at the moment they are looking for your products or services.
Since you attract people who are prepared to buy and you do not pay for each click, the return is much greater.
Even if you stop investing in SEO, your website will still appear on the results. Traditional advertising only works while you are paying for it.