When an activity like task is created from the Social Pane on the parent entity form, the system does not populate the Regarding field upon the first create event of the activity. Instead you can see from audit history that there's a second update event on the activity right after create, in which the Regarding field is filled with the reference to the parent entity.

This is a problem if you'd want to have a real-time workflow run right after a user creates a new task from the Social Pane. The workflow logic cannot reference any fields from the parent entity - or even be aware of for which entity the task has been created in the first place. Automation of any follow-up actions from the activity create event is therefore impossible, since it would only work in scenarios where the user creates the activity from the normal list view (even Activity Associated View), but not the Social Pane.

In my opinion, functional differences like this should not exist for a very core feature of a CRM platform, i.e. managing communication and actions towards business records. Especially when the platform contains a prominent yet uncustomizable UI component like the Social Pane.