If Google adds something to the Analytics Dashboard its important!
So what is Cohorts? Well Google says:
Cohorts will help you examine the behavior and performance of groups of users related by common attributes.
A cohort is a group of users who share a common characteristic that is identified in this report by a Google Analytics dimension. For example, all users with the same Acquisition Date belong to the same cohort. The Cohort Analysis report lets you isolate and analyze cohort behavior.
For more information about Cohort Analytics see: https://support.google.com/analytics/answer/6158745?hl=en
There are actually 2 new sets of analytics in Google Analytics that is; Cohort Analytics and Active Users. Both of these metrics can help determine user behavior on your site. Given the time I will try to write something about the "Active Users" metrics and how to use this to really expose weaknesses.
This is all very exciting stuff from an SEO perspective. Google is totally ramping up user behavior signals.
Check out what Google says about "Active Users" here: https://support.google.com/analytics/answer/6171863?hl=en
Since behaviorial metrics are a strong ranking signal this should be taken seriously by anyone who owns a website and SEOs alike.