One of the most tangible positives of e-commerce is the lowered cost. A part of these lowered costs could be passed on to customers in the form of discounted prices. Here are some of the ways that costs can be reduced with e-commerce:

Advertising and Marketing: Organic search engine traffic, pay-per-click, and social media traffic are some of the advertising channels that can be cost-effective.
Personnel: The automation of checkout, billing, payments, inventory management, and other operational processes lowers the number of employees required to run an e-commerce setup.
Real Estate: This one is a no-brainer. An e-commerce merchant does not need a prominent physical location.

Hope this helps!