Do you know cross domain tracking helps website owners specially ecommerce business to get the accurate data of customer? Many large company contracts with different brands for same products. therefore every brands have different websites. That means every website shows product to different customers.

Customers can perform view cart, add to cart, checkout on a particular website where they can view content(product descriptions). However when they go for purchase another landing page appears to them of another domain. As each website is different, so here would be 2 different google analytics cookie ID or GA ID. Therefore, it signals as 2 users. 

Do you think it is 2 users? Probably no. Thus cross domain helps the ecommerce businesses to track double user to single user. So, from google tag manager we can set the same measurement ID to both website. 

Step