In all the talk of graphical downgrades no one seems much preoccupied with 'why?'. Why build something and then proceed to tear it down, piece by piece, in the hope that ever more diminished expectations about the final product won't be severe enough to...
The timer is your biggest enemy. Get the high scores by finishing levels as quickly as possible.
That said, you don't die if the timer runs out. You just lose points.
You might have to backtrack to find all the coins.