This tells you the percent of each cohort that comes back every month. It is the number of new individual customers in each month who made 1 returning order.
It is a not cumulative metric.
The number of customers that came and made a returning order in the months after that first purchase. Do you want to know how many customers came back in that first month and placed another order? - This metric will tell you.
You might have a highly consumable product so you are curious if you have a natural loyalty to the product that makes them come back and purchase more. Or you have a drip campaign that tries to encourage people to return and make a purchase 1-2 weeks after their first purchase. This metric will help you see that activity.
If you are doing email marketing - you will be able to measure campaigns -- how many customers came back after receiving specific emails - by segmenting by marketing campaign. You can also see if a specific product is increasing the frequency of when customers come back.