Search Engine Optimization is the practice of Ranking a Website on the search Engines Results Page to increase its visibility when users search for Relevant Keywords and Queries.
As you can Increase the Ranking of a Site across a Range of Keywords, you will begin to see an increase in the Organic Traffic that it Receives. Organic Traffic is that which comes from Google's Natural Listings, Rather than Paid Ads.
Yes, your Business should be investing in SEO. Search Engine Optimization offers a way to increase Traffic without Paying for Each and Every Click.
When you run PPC Ads, you'll be charged for Every Single Click that comes to your Website through that Channel. However, if your Website Ranks Organically on the Search Engines, this Traffic is Essentially free (at least in terms of a Cost-Per-Click). Of course, it takes Investment into Skills and Resources to Rank a Website on the SERPs.