Almost all the apps you use sync with a server every so often on your phone. This could be your photos app syncing with the cloud to backup new photos you took or your messages app syncing with your telecarrier’s servers to sync any new messages.
Most of this is done in the background without necessarily telling the user. It’d be annoying getting notifications every few minutes that your apps are syncing with no new updates.
That said, a lot of times, apps will sync when you’re actively using them. This article discusses foreground sync, what it is, and whether you should care about being notified.
Foreground sync explained
As mentioned, Foreground sync is when the app you’re using syncs with its source servers in the foreground. Note that you’ll usually find this as a setting option in your phone’s notification settings instead of operational ones because it addresses whether or not you want to be informed of any active syncs.
Phones with this notification setting on will see a status bar in their notification shade informing them that a particular app is active and using system resources and foreground data. The notification cannot be dismissed until the app or either stopped or killed in the background.
Should you leave this on or off?
Unless you want to be notified every time an active app is syncing or using system resources — something that’s not very helpful in day-to-day usage, you should leave this setting off.
As mentioned before, notification settings like this are often set to off by default as they can easily annoy users with unnecessary notifications, especially if many apps are installed on the user’s phone.
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