What are the common uses of the roof pieces in the Sydney Opera House set?
You can see the inventory of the opera house on Brickset.

The majority of the roof pieces you seem to be concerned about are these bow pieces, of which you get 34 pairs and one extra left piece.



These pieces are fairly common and are used typically in cars, boats, planes, spacecraft, and other aerodynamic structures, as well as building roofs, robots, and other objects where you need a curvy shape. For example, the white pieces were used in a Ninjago copter set:



34 matched pairs is a lot of these for a normal person to have, so if you never plan to rebuild the opera house you might not use them all (though you could just consider it a challenge to come up with as many builds as you can that use these). However, the set itself has 2989 parts, so that leaves over 2900 pieces that are not white bows that you can presumably reuse in some other construction.