For those that clean up their collection of files after a shoot, what is your goal ratio of those kept vs deleted?
Very dependent on sujet and material.
With high speed stuff there is a lot of trial and error for example, while working with collodium coated plates makes sure you exercise greatest care. On the gripping hand you have commercial shots where the kept shot is selection is based partially on the rest of the content, which will only be created after the shot. So it's wise to give the art director some options.