People have covered other details.

One thing that I think gets overlooked because it's a relatively small detail comparatively is that Israel serves as a sort of test lab for the US armed forces & the US surveillance apparatus because they get to field test the highest-end military equipment in live conditions (e.g. the Iron Dome). This is invaluable to the US because Israel as the junior partner provides critical info and the ability to test and refine technology and techniques in a way that it wouldn't otherwise get the opportunity to.