Speed increases conversions. Nobody wants to spend extra time to complete a transaction, when offline or online. When customers are able to find the product they need and complete checkout quickly, conversions will increase.

In ecommerce, speed is often conflated with 'site speed'. The performance and speed of a site is vital, and it is still just one part of the equation. The process takes many steps, and reducing the number of steps reduce the overall time spent for a customer.

A high-converting site must deliver the most-compelling information in a streamlined manner in order to reduce the number of steps needed to complete the process. That includes making it easy for customers to find the right product, providing the right information, compelling the buyer, and providing convenient checkout options.

Shopify has a good post on technical ways to increase Shopify speed and mentions that a balance must be struck between performance and speed.

The trade-offs you make to functionality, experience, and design dictate your site’s performance, and it’s all about striking the right balance between performance and functionality. There is no one-size-fits-all guide for everyone. Helping you make the right tradeoffs for your brand is why we created this post.

There are tradeoffs and multiple factors go into the speed of an ecommerce site. Consider speed from both the perspective of both users and robots when evaluating optimizations.