Native Android notifications are displayed as heads-up, which disappear in a few seconds making it difficult for users to read and act on the message. Moreover, the notifications get grouped in the notification tray, making it hard to segregate important messages.
Truecaller notifications, unlike native Android notifications, provide better visibility into important messages by showing them on top of the screen and ensuring that they can only be dismissed by the user.To achieve this, Truecaller requires the "draw over other apps" permission.