You shouldn't be driving in 4 wheel drive on dry pavement, it can damage your car. But even in heavy snow you will have a larger turning radius.
The reason why it won't let you turn is because the wheels are locked meaning that they rotate at the same speed. When you turn your outer wheel wants to spin faster than your inner wheel, so something has to give, either the inside wheel will spin faster or the outside wheel will not want to move. when you over power the traction with the engine you will "plow" forward and not turn as sharp as your wheels are turned.
It takes 2 seconds to switch the Trac back to 2wd, this is what you need to do when parking.