So, what is traction? Basically, it is about upcoming patterns that indicate a scaling and repeatable business. Traction is an evidence of a sufficiently large market demand and more specifically about adoption and engagement. If you do well, traction is the confirmation of the hypotheses that you have about your product or service. Traction is about making actual progress and it is important in each phase of your app. It is about the first few early adopters that sign up when you just got started, and eventually it also is about the users that make (in-app) purchases. How well is your app doing converting people into users and users into customers?
Even emerging app clones (or copycats) are a sign of traction. It proves, along with your grown user base, that the problem that your app is solving really matters and that the problem is worth solving.
Things as profitability...