The primary benefit of SEO (Search Engine Optimisation) is a steady stream of traffic to your website.
Ads, whilst fantastic, deliver traffic only as long as they're paid for. Search engine traffic, on the other hand, continues to arrive long after content has been written and optimised.
If you're a local business, then Local SEO can help your business to rank at the top of Google for local searches.
If you own or manage an eCommerce business, eCommerce SEO can help your business rank at the top of Google for products and product category searches, earning you convertible traffic.