It would be useful to be able to isolate and analyse the behaviour of returning users as opposed to new users, for example to be able to see:

• how well we’re engaging existing users by showing the number of active users in a given time period that created their account in a previous time period, and being able to track this over time as a rolling cohort
• understand what activity is encourage existing users back to the product, e.g. if we held an event or ran a campaign would we see a spike in returning users specifically as a result
• how does the behaviour or returning users differ from that of new users, e.g. do users spend more or less time in the product on a day that’s not their first day? Do they use different features?

This is all possible with Mixpanel as you can create a cohort that did x event before today and set this on a rolling basis.