Job assignment

My boss's boss talked with me again.........mainly talking about other people.......but I found one point worth to note. He said that when a supervisor asked a subordinate to do this and that, especially long term jobs, the subordinate should think critically and carefully whether the jobs are good to himself, can help him grow up, or earn any merit. Why? It was because sometimes when the supervisor arranged work for his subordinate, he just thought of his own interests and would took advantage of the subordinate.......treated him as a "tool" only. In such case, the subordinate should voice out. Or, the subordinate should take the initiative to take up those jobs which are good to himself. I think that this is quite right sometimes.