QQ: Create Custom Dynamic Groups In Power BI - Advanced DAX


I am using the DAX explained in this video and everything is working fine. One thing that I would like to get my head around is the use of COUNTROWS. As I have now gone through most of the contents and am developing a few models, I am starting to use but I don’t fully understand it in its embedded use, such as this example. I would like to know what count row does here and what would happen if we had not used the count rows. That way, it will help me to know it fully and start applying it to other similar scenarios.
Thank you.

Please see here to learn more about COUNTROWS.