Estimate data used by your top apps.
App data has two components that respond to different fixes. Foreground traffic scales with how often you open the app and what it loads each time, so it falls if you use the app less. Background traffic — push sync, prefetching, location reporting — continues regardless and can only be cut in settings. Splitting them shows whether restricting background data would actually help or whether the usage is genuinely your own activity.
Foreground and background split
Foreground MB per day = sessions x MB per session; total per day = foreground + background sync; monthly GB = total per day x days / 1024
Divide the app's reported data usage over a period by the number of times you opened it, both of which are visible in iOS Screen Time and Android Digital Wellbeing alongside the per-app data figures.
Cloud photo backup, social feeds that prefetch video, podcast apps set to auto-download, and email with aggressive push sync. Restricting background data on those four usually recovers most of the avoidable usage.
Generally no — push notifications arrive through the operating system's own channel, which is exempt. What stops is content prefetching, so the app takes a moment to load fresh material when you open it.