Let me intr our seminar project about MTL. The motivation comes from a scene that in a company, different departments could have a need to classify user's label with various but  similar data set. The diagram shows an example of such scene.

The Depart 1 works on Video Recommendation who cares more about user interests, since their primary goal is to increase users' satisfaction to increase retention and duration

The Depart 2 works on Live and Sales who focus on Purchase Intention of users. Since their primary goal is to increase sales.