We need to sync your Flo data every once in a while because all your trips are saved in the cloud. However, we only sync your data when you're on Wi-Fi, not when you're using your cellular network, so you don't impact your data plan.
In "Settings" you can tap the box next to "Sync over wifi only" to turn it OFF (the default setting is ON). If you do that, Flo will sync your data after every trip, whether you're on Wi-Fi or the cellular network. That's handy if you travel a lot and don't mind using your data plan to sync.