If your remote code writes any data to Share Point (e.g.
adds a list item), you’ll notice that the Share Point user interface makes it clear that the list item was added/modified by an app.
Effectively, we lose the information which tells us which actual person was involved in the change - in some circumstances, this could be a problem if some kind of audit trail is required.
To make things clear, here are two screenshots which show the difference: List item added by "app user" authentication: List item added by "app-only" authentication: If you’re wondering how Share Point/Office 365 deals with this under the covers, you’ll find that all lists now have 2 new hidden columns - “App Created By” and “App Modified By”.
The vast majority of MSDN and blog samples use this approach.
This is ultimately the problem - “user app” authentication does not currently work for events related to the host web.
So to work around this we need a different approach.