I guess it really depends where. I believe here, where WhatsApp is pretty much the _only_ method of communication, people most definitely check it every few minutes, and especially before they go to bed.
The notification and icon badges help hide when you're sleeping, but they advertise when you're interacting with someone. You're "unseen" for twenty hours. The guy you're cheating with logs in and sends you a message. Five minutes later, you log in and read it. You wait two hours, read it again and send another message. He doesn't check for an hour. You're so longing for his response, so every five minutes you're logging in "how many ticks? what color? has he read it yet??". Once he's out of his meeting, he (finally noticing the notification) logs in and sends a message. Your activity drops off now that you have your reply, but you nevertheless send yours...
Related question, does WhatsApp send the heartbeat only when I open the app, or every x minutes as long as it has a network connection?