Activity Tracking enables you to view how much activity was tracked by a particular user while they were tracking time.
Learn more about it here: How Are Activity levels Calculated?
If you disable Activity Tracking for your organization, then you shall get no information on the activity levels of the team members tracking time.
You can enable/ disable tracking by following the steps as follows:
Click on Settings from the main menu, then select Features from the drop down menu. Click on the Activity tab and select Record Activity.
Click “Yes” if you want to enable it, or “No” if you want to disable it.