Mobile and desktop conversion rates are influenced by two main parameters. The first is traffic influencers—this can be things like channel mix, marketing campaign, seasonality. The second is the performance of the website, for example UX and site speed. Any of these can cause your mobile or desktop conversion rate to go up or down.
The benefit of using Rel mCvR to evaluate your mobile performance is that traffic influencers tend to not impact the metric. Why? Because the same campaigns and seasonalities will reach both mobile and desktop versions of your website, a good marketing campaign will make both the mobile and desktop conversion rate go up but leave Rel mCvR stable. When you evaluate the metric over time, it will show us if we have improved our mobile website.