CO selector - persistence of selected CO

Once a CO is selected, it is forgotten if the user navigates to a page that belongs to a model that does not require a CO (and therefore will not have it carried in the URL for following pages). Is there a benefit to forcing users to select a CO every time they return to the main menu (or some other non co specific page)? How often are users expected to want to change the CO to a different one?

How will this be implemented if it is a desirable feature? One option is:

$this -> Session -> write("currentCO", $currentcoid);