If I may have a bit of your time, usually sales like this are pre-arranged. Billionaire goes to a Bank (like GS or whatever) tells them I need to sell X number

If I may have a bit of your time, usually sales like this are pre-arranged. Billionaire goes to a Bank (like GS or whatever) tells them I need to sell X number of Shares by Y date on Z price, the Bank gathers up the buyers, and then the the transaction is committed in one fell swoop, on market down, GS takes their commission and it's over by the time the markets open next Monday What are the pros/cons of doing this bit by bit, over such a long period of time, on the public market? He is still not done and will be selling well into next week.