All that happened with Foursquare/Swarm was that the user had to press a button to download another free app. I agree it was a silly decision, but was ultimately just a 40 second inconvenience.
Unless you're offering a large value proposition that the consumer finds it difficult to say no to, you just elaborated one of the biggest challenges companies face.
Whether one regards it as absurd or not, that 40 seconds makes a big difference (not to mention people don't like change very much once they're comfortable with a thing they use). It's in that 40 seconds that the consumer shrugs and says to their self: meh, I don't feel like it, I don't want to deal with this new app that I don't understand, my phone is already cluttered with apps I don't use.
Shopping cart abandonment due to second thoughts on purchases. Drawn out check-out processes. Long sign-up forms. Slightly slow web page load times. Waiting in lines. Every study comes back with the same conclusion on consumer behavior: those seconds matter a lot.
I use it to read tips about places I visit, which are often useful especially when deciding what to order upon first visit.
I use the social features among a small group of friends. Facebook has similar features but is useless for me as I rarely use facebook, and I am very sensitive about who can see my check-ins. Being a separate social network allows me to curate that list very carefully.
Plus the lifelogging aspect has proven itself useful many times. When you want to remember that awesome meatball restaurant in Amsterdam, nothing beats looking at a list of places you've actually visited. (https://foursquare.com/meatballsnl)