Organic search traffic is one of the most important traffic channels you can use to drive in potential customers.
Not only does it tend to convert better than paid ads, it also enables you to lock in a steady stream of traffic, day in, and day out.
By getting your site to the top of the search engines for your target keywords, you're practically guaranteed to drive in a steady, predictable stream of hungry shoppers.
I don't know many marketing channels that enable such longterm growth, and that are not out of reach or budget.
With a good SEO strategy, your ecommerce store can develop awareness around your brand, and expand your sales volume to numbers you couldn't previously achieve.
One thing I know is my clients tend to sleep much better knowing SEO traffic is coming in daily, regardless of whether they invest or not in another form of marketing.