Whats wrong with leaving it checked on "Partial optimization for theme CSS development"
on a production site. We are never going to modify core drupal css or core module css. I will only edit the theme css in the future. I read people say you should set it to 'Full optimization' once your done modifying your theme. But another admin may come in one day and edit our theme style sheet and wonder why his changes are not taking effect. The site loads fast enough as is.