When it started in 1995, it seemed like a good place to find friends from schools. That ended in 2015, when it was acquired by PeopleConnect, which uses Classmates.com to generate subscriptions for its other company Intelius.
Here's the user experience: You enter your schools, and they will display the classmates from your years there. The problem is that Classmates does not have your classmates in their database unless those classmates have registered on classmates.com. I listed 5 of the schools I attended and less than 2% of my classmates were in the database.
You can do an extended search for unlisted classmates, and it returns "0" results, with prominent CLICKBAIT to "find them using the Intelius service". You will wait at least 5 minutes while watching progress bars telling you that the service has found them, and compiling their criminal record, family members, residences, financial history, social media. AFTER 5 MINUTES OF WAITING, you get a screen to sign up for Intelius subscription service.
THAT IS THE REASON CLASSMATES IS STILL ONLINE, TO SERVE AS AS CLICKBAIT FOR INTELUS.
CLASSMATES.COM IS USELESS, and is FULL OF OTHER 3RD PARTY CLICKBAIT under every button, and on all sidebars, and pop-ups. If they ever get your email, they will bait you weekly with "one of your classmates says hi"