Sometimes you'll have lots of instances of a particular action or occurrence, and you might want the earliest or latest instance only. You can get this using the max or min function. 

For example, here I have all the reservations made by customers, but some have made multiple reservations:

If I only want to see the first reservation for each customer, I can use a summerize step to get the 'min' of the reservations (the earliest reservation per customer).

Now I can do further calculations, for example, a row count broken down by month, to see how many 'first' reservations were made per month. 

To get the most recent reservations, I can do the same steps using 'max' instead of 'min'.