For MIDI music composing.
Development of MIDI sequencers kind of plateaued and stalled sometime after DAW (digitital audio workstation multitracking software) hit the market. After that, MIDI sequencer software didn't get any R&D time, so they didn't get better - and actually may have gotten slightly worse (latency) with all the abstraction layers between the hardware and software on current OSes.
Bars & Pipes on the Amiga is still the best MIDI sequencer and the fact it bangs the hardware directly makes the Amiga a great, tight, MIDI composing tool.
Also, with trackers and the Paula chip, some consider the Amiga a musical instrument with a distinctive sound. You don't just stop using an old instrument especially when it has character (like a Les Paul guitar or a vintage tube amp) - you use it because of its special sound (and that's something that even emulators can't copy - even though I am big fan of UAE).
