1. hashchange/single page application/ measuring multi-page application systems where the url does not change.
2. measuring in an angular environment using listener functionality
3. video milestone measurement using direct call rules.
4. AJAX calls
5. Fire direct call rule when object is not NULL
6. Firing event which is not available as event pre-set
7. Firing direct call rule from event base rule
8. In case of iFrame

Reference: https://www.digitalbalance.com.au/our-blog/how-to-use-direct-call-rules-in-dtm/