You do not need to leave the app open to mine. Pi does not affect your phone’s performance, drain your battery, nor use your network data any more than other regular apps. Once you hit the lightning button that initiates a new mining session and confirms your security circle, you can even close the app and you will continue to mine Pi. However, making diverse contributions to the network, such as using Pi apps, running computer nodes or inviting friends, will boost your mining rate. Any mobile usage of Pi apps will not consume more energy or resources than other regular mobile apps.
So how can you mine a cryptocurrency without draining your battery or data? Instead of burning energy, as proof of work cryptocurrencies like Bitcoin do, Pi secures its ledger when members vouch for each other as trustworthy. For more information, please refer to another FAQ – How can Pi be mined on mobile phones without energy consumption typically known in “crypto mining”?