The functions of Android smartphones, such as location information used in apps, emails, and map apps, and Google services are inseparable. In addition to Google, there are many companies that provide online services such as SNS and streaming, and support the functions of Android smartphones.
Users of these services always have "accounts", and they are authenticated as valid users by their user ID and password. The "Account" screen of the Settings app is for centrally managing such accounts, and multiple accounts such as Google accounts are registered.
A switch called "Automatically synchronize data" is provided on the screen, and the registered account controls the automatic update of data by the related service / app. If this switch is on, the registered account will always be up-to-date, and if it is off, it will be updated manually (the last time you used the service / app).
Turning off the switch saves data traffic and power consumption by eliminating the need to periodically send and receive data. However, if the freshness that you want to keep synchronized with the server always contains important data, turning it off uniformly will reduce the convenience. You'll want to be careful, as you won't receive notifications when updates occur.
In addition, tap "Account item" → "Account synchronization" in order and tap "Account synchronization" that appears to narrow down the items to be synchronized. Google accounts allow you to turn on and off services such as email and calendar individually, so we recommend that you use this instead of controlling all accounts uniformly with the "Automatically sync data" switch.