On behalf of brianh who is unable to post here.
No one has covered the most significant reason why the turn onto final should be by 500' minimum. It is because this turn is the regular cause of stall/spin accidents due to crossed controls in an overshoot past centreline while on base. The danger of crossed controls is exacerbated by the "proximity to ground" effect on pilot mindset, therefore the pilot tends to cross control to track back to centreline rather than make a steep turn near the ground.
500' minimum gives some small chance of recovery, and less chance of ground proximity illusion creating the problem in the first place.
Unfortunately, this situation is not well covered in most pilot training where stalls all seem to be at high altitudes and high nose attitudes and so many victims do not realise the onset until very late in real life, particularly as their eyes are outside the cockpit on the arrival threshold and they miss the fact that the ball is way out to one side and airspeed decreasing. It is well covered in Schiff, I think Vol 1 and is a renowned cause of arrival crashes and death in light aircraft..