At the time of writing, it was named Potential but now it's named Priority. The meaning has stayed the same though. What I tend to do is focus more on the Organic CTR because if the Monthly Volume has "no data" it will make the Priority score very low. You can change this by applying your own modifier in "My Score" but it depends on what your Potential cut off is. E.g. I won't target any keywords under a Potential of 40.

There is data out there that gives you a CTR estimate based on the SERP position. For example, position 1 gets approx 34% clicks, position 2 gets approx 17% clicks etc. I wrote an article on this a while back for desktop and mobile CTRs > https://mechanised.co.uk/seo/does-being-at-the-top-of-google-make-a-difference/

So using the Moz CTR data you know that 100% of searchers click on organic results and 34% of the clicks go on the first result.