I think the calendar is supposed to give you a overview of your tasks with due dates set, which is of cource nice. As it is said on the calendar page, you could also see this in Google Calendar if you prefer (but the iCal-connection doesn't work that well).
My main objection to the caledar view is that the completed tasks show up at the due date rather than the completed date. Clearly this must be a bug, Toodledo??
A little request: Show completed tasks on the completed date, and specify how many that were over due like this:
"X Tasks Completed On Time"
"Y Over Due Tasks Completed"
I also think the the completed tasks should be exported in an iCal-connection, but maybe a different one?