[cellis]

There's lots of problems with this line of thinking. One, it encourages "butt-in-seat" thinking, which is inefficient. If I deliver what you wanted delivered in the time allotted, I should be free to work on whatever I want. Of course, a manager wants to squeeze every drop, so if you've finished they'll say "I have some more work for you". But best believe you'll never be fairly compensated for that work ( at most companies anyways. Obviously if the company is Facebook/Google you can have a massive impact and will be flying around to work on whatever suits your fancy ).

Look at it from a contractor's point of view: a contractor will have many other things that they can deliver and make money from, so adding a bit of polish to your project vs delivering another client's makes less sense.