The downside of any application is that is has a lifespan. There is the initial launch, the hype phase, the use phase, the loyalty phase and then the legacy phase. How fast an application goes through these phases can vary, depending on how much relevance it can muster, but all apps will eventually die off. The way you keep an economy going is to keep innovating and developing new products to replace those that move into loyalty and legacy phases. This is why capitalism thrives on competing products.