When a person changes the fields of a multi-select type custom field (and the recently added ‘People’ field, the activity log notifications, currently, do not clearly define what exactly has been changed (for Inbox notifications, the Notify task collaborators when this field’s value is changed needs to be enabled). Both Inbox and activity log display the same but it is not concise…
Current situation:
Option A, Option B & Option C are already selected from the multi-select field’s options.
If someone say adds Option D, the activity log will say:
X user changed [multi-select field name] from “Option A, Option B, Option C” to "Option A, Option B, Option C, Option D
Ideal situation:
As per above, but instead the notification in the activity log would say:
X user added Option D to [multi-select field name]
Alternatively if Option C was deselected, the activity log would say:
X user removed Option C from [multi-select field name]
Would that not be much simpler and easier to read and understand?
Imagine we had hundreds of fields preselected and then adding/removing… 
This notification issue applies to both the Multi-select & People fields.
Due to the above issue, we have all our notifications for mult-select fields disabled because the notifications in Inbox and activity log are not easily legible.
I hope this can be a quick fix!