Depends on the business. I've worked some places where the best thing the company could do was make sure the boss was away permanently (and then replace them with someone who does not require a sphinctal cranial separation). I've worked others where no boss meant nothing got done but net surfing and gossiping.
Sometimes. Mine was always the same, I worked the same whether the main boss was looking over my shoulder or I was in the store alone, but some people get stressed when the boss is there. They get afraid of messing up and end up screwing everything up. But, some take that as an excuse to goof off. I think it depends on the worker.