text: articles - Why do we have to use a determiner "their"? - English Language Learners Stack Exchange
  To begin with, I think, the reason why it is vital to work in a desired profession is that people spend a major amount of their time at their workplaces, so job satisfaction becomes an important aspect of life.
  An Ielts teacher corrected the above sentence by adding their. If it is right, then Why should we add their in the sentence? Could we omit it?
  Nope, you can't omit it. As to why: determiners were so named for a good reason: they allow us to determine what's being talked about. In this case, specifically which workplaces (the ones belonging to the specific people in question). – Dan Bron Sep 30 '15 at 12:16
  Because it refers to offices, factories, retail establishments, etc. that is, to the actual physical places where people work, the word workplaces was not really the proper word choice in a sentence about desirable professions. Profession refers to the nature of the work.
  What is needed is a phrase that refers to the time spent working doing what one does, not a word that refers to the building or establishment.
  People spend much of their time at work.
  That revision makes the question of whether to use their moot. But the reason why the original had been corrected to include their is that we want to stress the idea that people are spending time where they work, not merely where work is being done.
  Yes, you can omit the word "their".
  Including the "their" clarifies the sentence. It makes it clearer that you are talking about the time people spend at "their workplaces", as opposed to other people's workplaces.
  Some people spend a lot of time at other people's workplaces. For example, travelling salesmen, shoppers, and sports fans.
  answered Sep 30 '15 at 12:20
  You don't necessarily need it, but it makes a little bit more sense because if you just say "in work places" rather than "in their work places" it does not specify whose work place it is, and therefore where it is at all, because there are millions upon millions of different work places.