Lieutenant General Timothy D. Haugh is very clear on section 702:

"In my experience it is absolutely essential," he told lawmakers.

New York Times on Section 702: https://www.nytimes.com/article/warrantless-surveillance-section-702.html

A very "good" designed power point of section 702 by the US government: https://www.dni.gov/files/icotr/Section702-Basics-Infographic.pdf

The law text and section 702 (page 4), I had to search way too long to get to that, mostly you just find an overview by a three letter agency to justify the section. It is like the government does not want that you read it in full: https://www.congress.gov/110/plaws/publ261/PLAW-110publ261.pdf