The PIN adds a layer of verification to ensure no one can get access to your account, even if they have access to your phone. For example, if your phone is also used by others, and if they launch the CoinDCX app, they will be asked to enter a 6-digit PIN to get access. Since the 6-digit PIN is only known to you, they will not be able to access your CoinDCX account on the app.
