It beats the hell out of either laptops or phones, for me, for these tasks:
- Music. Excellent as a sheet music display; can record and edit midi quite well; play tutorial videos; act as a tuner, tone generator, or metronome (my phone beats it on that front due to portability, but still, if I already have the iPad out on the stand...); plenty good enough at audio recording and editing for my extremely-amateur purposes, plus its ability to play loops and beats and such.
- Reading. It's especially amazing for comic books (in landscape mode a 12.9 incher is almost the same size as an open comic book! You can read two-page side-by-side on it, no problem) and PDFs. I prefer iPad mini sized devices for prose books in ordinary ebook formats, but the 12.9" pro is damn near perfect for those two things. Laptops and desktop computers also work for comic books and PDFs, but are a pretty big downgrade, UX-wise.
- Drawing. Obviously.
- Long-form writing. Laptops work great for this too, of course, but you still need a separate keyboard if you want decent ergonomics. iPad doesn't have an attached keyboard taking up space that I could instead use for a separate keyboard.
It's also just as good as a laptop (to me) as a remote SSH terminal, VNC terminal, video/music player, web browser et c. I can't really think of much I do on my (personal! Not work-supplied) laptop that I can't do just as well on an iPad, maybe supplemented by a headless RPi hanging off my router, or a cheap VM rental (or just the Linux server in an old desktop workstation tower that I already have anyway).