It guarantees you a coveted spot in a TSA Precheck line, and you will be able to skip immigration lines on your return home from international destinations. (rewardexpert.com)
NOTE: Be sure to click here to see all recent TravelSkills posts about: Avoiding long customs & immigration lines + UberX, Lyft at LAX + Binge drinking on business? (travelskills.com)
This means that you won't have to wait in the usually long immigration line when entering the United States. (uponarriving.com)