What's the big deal with going home when the work day ends?

If the work day is 8:30 to 5:30, Some ridiculous management people/bosses get very upset if people leave at 5:30. What the heck is wrong with that? As long as you get the work done, who cares. People have lives and everyone utilizes their times differently... so who is one person to get upset if someone goes home at 5:30.