Automatic updates in the Offline & Sync tab default to being on.
There are two things that happen when automatic updates are on:
When a user makes changes locally, the change starts being pushed back to the server. If the device is connected, sending will be attempted; if updates fail it will take longer. When working normally, this happens immediately.
It takes about 30 minutes to read back the latest data from other users' changes. Changes are applied to a particular user's app when they navigate away from the place where the change was made. The 30-minute timeframe exists so as to mitigate the amount of work for the server.
If you turn automatic updates off, you have to sync changes manually. If the updates aren't happening, that's a sign you may have an error and need to sync manually as well to figure out what's going wrong.