Even a tiny increase in overall search result quality might have a noticeable effect on conversion rate. Naturally, you can use exit-rate to judge if your search needs improvements and do required adjustments, but will you be able to make sure those changes are safe? What if improved relevancy for a specific category breaks search for several other categories?

Moreover, high exit-rate means no matter what you are going to do, the problem has taken place, so dozens of customers already didn’t manage to find what they were up to. Basically, the only way to proceed is to have a reliable search quality validation approach.