The reason to collect and analyze metrics is to help make a decision.
No decision, no point in collecting metrics.
Sometimes you'll want to collect metrics ahead of time though. That way when you're ready to make a decision, you have enough historical data to support you.
That's why every website installs Google Analytics or a similar traffic tracker. In the early days you don't have many options for decision-making but 5 years down the line, having 5 years of data accumulated becomes valuable.
That's how Repeat Customer Insights is able to create historic reports for your store even if you just installed today. Shopify saves a bunch of order, customer, and product data just as part of its normal operations. So when Repeat Customer Insights gets installed it can go back through all of that data to analyze it and pull out recommendations for you.
All that historic data ends helping the analysis and supporting the decision making that you make in the present.
Because that's the point of it all. The decision making you're doing now, and where you're taking your store in the future.
Use cohorts to find out who the best customers are in your Shopify store
Repeat Customer Insights will automatically group your customers into cohorts based on when they first purchased. This will let you see how the date customers bought would impact their behavior.