Asynchronous After event that occurs after an existing item is changed, for example, when the user changes data in one or more fields.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
The ItemUpdated event can be used in response, for example, to a form edit, a data sheet post, an object model call, or a Web service call.
When you add a new item, only the ItemAdded() event is raised. However, in cases where Explorer View is used, both the ItemAdded and ItemUpdated events are raised. In such cases the ItemUpdated event always occurs after the ItemAdded() event occurs.
Before and After properties are guaranteed for post events on documents, but Before properties are not available for post events on list items.