Whenever a trendy app comes along, there are people who ask, “What is the point of this?” If millions of people are using something, there has to be a reason. In our What Is the Point of... series, we’ll explain it to you.

This week, we're asking, What is the point of Foursquare?

Yes, we know. The check-in is dead. If the polls are accurate, most people don't even know location apps exist. So we don't have to care about Foursquare, right? Well, no. As of last month, the service had 20 million users, or about half an Instagram. It's not for everybody, but it has its devoted fans.

Why, though? Isn't Foursquare just for spamming Twitter and Facebook with what Geoloqi's Amber Case calls "geoloquacious" noise about your trip to the grocery store? It can be, and for too many users, it is.

But turn all that off. Forget the annoying badges and mayorships, too. There's one useful thing at which Foursquare is very, very good: recommendations.

Use Foursquare Quietly

Seriously, you can ignore all the gamification in Foursquare. No more "You unlocked the #SuperSpamAttack badge!" No more "You ousted your mom as mayor of your basement apartment!" Do it. That stuff is pointless.

You can (and should) also turn off the auto-broadcasting to Twitter and Facebook. Sure, you can share a meaningful check-in every once in a while, but no one cares that you refer to your apartment as ThaChillZone. In fact, close off Foursquare to everyone except people you actually know.

More importantly, only be Foursquare friends with people whose tastes you trust. That's when Foursquare starts to get interesting.

Use It to Explore

There are lots of apps out there to recommend local stores and restaurants, because that's where all the mobile money is. Google, Facebook, Yelp and countless smaller companies all try to do that. But Foursquare, probably due to all the gamification we all turned off a few paragraphs ago, has great data for recommendations because its users check in intentionally and leave helpful tips. It also has the best UI around for place recommendations.

In addition to getting recommendations from your friends, which is the basic use case for Foursquare, there are two killer features: Explore and Radar. Explore lets you search for places to eat, shop or stay nearby, and it can personalize the results to you. So checking in to places you like, even if you aren't broadcasting it, helps you find more places.

You can even use Foursquare Explore on the Web, and it looks awesome on an iPad. (Hopefully, they'll make the map tiles retina-ready soon, and then it will be heavenly.) So discovery on Foursquare isn't just a mobile activity anymore.

But Radar (iPhone only, for now) uses the smartphone's capabilities to their fullest extent. If you turn it on, Foursquare will send you push notifications in your pocket while you're walking around, letting you know about nearby places. So you don't even have to have your phone out to find a restaurant you might like. Checking in on Foursquare can get you discounts on things, too.

Even if geoloquacious Foursquare use drives you crazy, you might find it worth your while to use it for quietly exploring and recommending things to close friends.