To practice turning pages for yourself even though both hands are busy playing.
To practice changing registration by hand even though your organ has pistons and toe studs.
To practice playing your pieces on various manuals and manual combinations.
To practice playing your pieces (or a part of the piece) one octave higher or lower with appropriate stops.
To practice adjusting to lower or higher bench even on your own organ.
To practice adjusting to different pedalboards (flat, radiating, wide or narrow).
To practice adjusting to different keyboards on mechanical action organs.
To practice keeping your composure and focus after various mistakes when you play in public.
Take measured risks. If mistakes aren't fatal, you can learn to be a little braver again and again.