Big news overnight on the app front was the sale of WhatsApp for $19 billion. Yes, an app for $19 billion.Of course, this isn't any app. This is a hugely popular messaging app. Popular means consumers which means value. Hence the monstrously high price tag here.Of course, the big concern for users is just how this sale will impact them. Right now, we don't know, although Facebook is making all the right noises. Also, if we use the Instagram purchase as a guide to what will happen, you are unlikely to see too much interference from Facebook in the short term.Facebook has confirmed it will keep a degree of independence, with the chat app keeping the same brand and company structure. However, it will have access to Facebook's 'expertise, resources and scale' over the longer term.Why has Facebook bought it? Well, it maenads no one else can have the popular app, which eliminates a level of competition in the networking and chat field. But it also gets access to more people.Facebook isn't really seen as 'cool', but WhatsApp is. It is also very popular, with 450 million users, 315 million of them active, with a growing presence in emerging markets. That will certainly help boost Facebook's customer base.But with the app said to be staying app free, you do wonder how Facebook will get the money back (and make some more). We'll probably only discover that over the next couple of years. In the meantime, you can rest easy. Nothing obvious is changing with WhatsApp.