The improved notifications system allows you to receive email updates on mentions, invites and comments for items that you follow.
In-app notifications allow you to receive updates when you are added or removed from a workspace, you are assigned to an item, and when an item you are watching or assigned to has been commented.
The item activity log allows you to look into almost every update that has been made to a particular item since its creation, no matter if the item has been added manually by a team member or if it has been added/imported via an integration.