Organic click through rate is nothing but the ratio of searchers who click on an organic result in the search engine results pages to the total number of searches for the term that was searched by the user.
As for why it’s important, where do I begin?!
Firstly, it improves your website traffic without you making any active efforts to influence your ranking in any way. On top of that, it then also boosts your ranking significantly, again without any particular effort from your side towards the same. Most search engines, including Google, use click through rate as a metric to deduce whether or not a particular search result is desirable to a user.
So, to summarise, higher number of organic clicks on the search result corresponding to your website means that your page is ranked higher than other, which in turn leads to even more clicks and so on!