Can a Captain (or anyone for that matter) just decide to "simply moved forward a bit"? This isn't a compact car pulling off the roadway to the curb. This is a huge aircraft with zero visibility other than out the front windows, hence the need for ground crew. Plus the danger of jet engines to anyone who may be on the ground near them. I doubt they are permitted to move even an inch without authorization. But hey, I could be wrong and I await those to tell me I am. But it seems to me that a Captain can't just decide to fire up the engines and move a 737 because he thinks it might be a good idea.