Text entry. I find Musescore terrible (even revisited it after their huge upgrade). Being able to freely enter text means I don't have to care about timing and just get the notes on the page, which most other notation apps are strict about.

Nothing else comes remotely close to the engraving and scripting features.

Much more robust engraving support, and, frankly, being actually open source as opposed to owned by a big conglomerate who's gobbling up music companies right and left.