Your application may have multiple dynamic URLs executing the same operation. For example, viewing a user profile is a single transaction, but the URL varies with respect to the user.  

In such cases, you can group these URL to effectively monitor the performance of each.

In the above example, the same transaction invokes multiple URLs, since each individual checks their own profile. This actually clutters the monitoring environment and can be handled more effectively by grouping them based on their similarity. 

By default, APM Insight groups alphanumeric characters in dynamic URLs. You can also set up grouping for custom transactions.