Let's bring in an example.
Let's say you're an on-demand lawn mowing service, and you recently developed a mobile app to help people order your service. After you've established your business in the marketplace, you can continue to market that particular service and you'll probably generate revenue for as long as people have lawns.
But you already have a base of customers, and you know a few things about them (market intelligence) - they have homes and they care about the aesthetic of their homes, they like using mobile applications, and they have money to spend. So why not branch out and re-market to your existing customers? It's much easier to market to someone who has already purchased your product, because they already have faith in your company. Going out and finding new clients is a little trickier. It's time to growth hack: start offering window cleaning, landscaping, painting, or another home care service.