WhatsApp mode is a feature that helps users save on mobile data costs by allowing messages to be sent and received over Wi-Fi. WhatsApp mode works by reducing data usage when transmitting messages over the Internet. It does this by compressing media files like photos, videos and voice messages and only sending the most essential data for the message to be received. This reduces the amount of data used, making it much more economical for users to stay in contact with their friends and family.