The conversion rates from someone visiting your site to making a purchase of whatever product you're selling is incredibly important in terms of revenue. You've already spent money getting the person to your site, you just need to close the deal.

Things like sliders or just generally poor design can have a big impact on conversions.

If you tracked usage of a range of ecommerce themes you could probably find a way to know which ones had great conversion rates and which ones didn't perform so well. So now when people are looking for a new ecommerce theme they can filter by the ones with the highest conversion rates.