Setting aside the fact that this thing just sounds amazing, the performance mode alone is perfect for creating more expressive songs, and allows you to improv new takes on your existing tracks on the fly
This is the one thing (outside of the software that runs on it) that I would say is the only truly necessary item on this list. I could write music with my mouse into the piano roll and still make noises happen as long as I have you, lappy.
A creative powerhouse for songwriting and inspiration
Most of my writing gets done on this little powerhouse. Even when the song ends up transitioning to a DAW and completely different instruments, nothing quite helps me create like sitting down with this machine.