Thewintersnow you summed up all my thoughts about GP
For me it's the best way to quickly write a song. I jam with my guitar, and when I get something, I write it, idem for the bass. Then I write the drums. I can write a drum part so fast that I prefer opening GP to write it and export its midi to my DAW project, instead of writing it in the Daw which takes too long for me. Then I adjust in the DAW, if my drumkit is more complicated than the standard midi one.
It's also the best way to train on hard parts for me ,just mute the solo, and use the tempo trainer.
And, best way to write with another writer in your band. I have a friend who likes GP too, and we are fucking efficient in songwriting together, because we can send to each other the file, add ideas, cut, edit, and send again, until almost done.
Of course, it's not the best tool for more groovy styles. But it's handy, and I feel that working both ways (reading, and by ear) is really helpfull.