Our work is kind of tedious, and if you do fast work, you are given more work, so everyone is working at half speed (what a waste, I know) just for the paid time to finish and so, for us to go home.
What you say is strange to me, as a way to work in a company. We never finish early.
I think it depends on corporate culture in many cases too. I don't have to track my hours to get paid, as long as the work is done, I get paid. If I do extra (which is necessary sometimes), I get those hours put in a time bank.