Dropping, or "Throwing" the rod onto the ball (3 times) was the military way of loading, by the numbers. In the accuracy department, throwing the rod onto the powder was discouraged as it 'mealed" the powder (compressed and ground it up) thus changed it's burning characteristics - effecting accuracy.
The military did this to ensure the ball or bullet was on the powder even in a fouled barrel.
The Tige and Delvinge chamber's (Austrian and French) in the mid 1800's needed the rod used in this manner, to expand the undersized ball out into the rifling.
Some people still do this today - without knowing why - someone taught them to do this, obviously, while others do it as they are paranoid about getting the ball onto the powder and compressing it to the point the rod attempts to bounce out of the barrel. This ensures the ball is on the powder and that the powder is a single compressed pellet.
Some accuracy minded individuals seat the ball onto the powder and stop, using only enough pressure to get it there and no more, "lightly set".
Others seat the ball to a physical mark on the rod - every time, exactly to that spot and no more, no less. As power fouling builds in the chamber area (for those who do not wipe), the mark will attempt to climb above the muzzle's edge, as the fouling builds, shot after shot. Over a day's shooting of 50 or more shot, this could be as much as 1/4" higher. Attempting to still seat to the mark under these circumstances will cause increasing powder compression along with mealing of the powder.
Any mealing of the powder will change powder burn rates and larger changes in velocity and pressure, shot to shot - unless this is done exactly the same, shot after shot.
When I seat the ball with the rifle's hickory rod, I seat it to the powder, then put the starter knob over the end of the starter, then one bump on the knob with my hand to firmly seat the ball on the powder. I do this the same each time - which shows up in my chronographed velocities as less than 15fps difference high to low for a string of shots. The close the shots are in speed, the greater the accuracy "potential".
I found that if the ball is lightly seated on the powder - (you can feel when the ball is on the powder) and no more, the chornographed results average 100fps lower than when I use the single compression hit of my hand on the starter knob which transmits this force to seat the ball firmly on the powder. The difference (in rod height) is about 1/10" of compression, which, incidentally, the amount of compression most of us use when loading BP ctg. for our buffalo rifles.
This video shows my method of loading a VERY tight ball and patch. In this instance, I've fired over 50 shots on the trail that day, without ANY wiping & am using a .0225" patch and a .445" pure lead ball. This was the last shot of the day, done for the video. The other fellow is Hatchet Jack, shooting his 20 bore smoothie - note - he throws the rod, I do not. He usually throws it 3 times, however I see he only did that twice this time.
Some have stated, under the right circumstances - ie: HOT, hot day, hot barrel, that throwing the rod onto the powder can cause a detonation or ignition of the compressing powder - that would be disastrous if it happened.