All sites have a home or "root" page, which is usually the most frequented page on the site and the starting place of navigation for many visitors. Unless your site has only a handful of pages, you should think about how visitors will go from a general page (your root page) to a page containing more specific content. Do you have enough pages around a specific topic area that it would make sense to create a page describing these related pages (for example, root page -> related topic listing -> specific topic)? Do you have hundreds of different products that need to be classified under multiple category and subcategory pages?
If Google finds two identical pieces of content, whether on your own site, or on another you’re not even aware of, it will only index one of those pages. You should be aware of scraper sites, stealing your content automatically and republishing as your own. Here’s Graham Charlton’s thorough investigation on what to if your content ends up working better for somebody else.
Organic search is extremely important for online retailers, as many studies suggest it drives around 50% of website traffic. When it comes to search engine optimization for eCommerce, marketers get obsessive about testing all methods available to them to try and achieve higher rankings. The logic is very simple: higher positions on SERPs automatically result in higher impressions and a significantly better click-through rate. More people visiting your store should ultimately translate into better conversions and higher revenues.