I always build a song on one instrument to begin with - currently, my Tempest or my Electribe 2. Not on the Octatrack.
When I’ve got enough of a structure going, I sample what’s appropriate from the instrument in question into the Octatrack - drums, soundfx and so on. Nothing with harmonies, though - I keep those sections in the instrument, since I want to keep working on the song after I’ve connected the Octatrack into the workflow.
From here, I keep developing the track, but now I bring in sounds from other sources as well. Anything goes from this point. Other drums, sound fx, harmonies that work as repeats, and I mash it up. I use the fx to bring all sounds together and I always use track 8 as an fx track as well.
I usually build songs with lots of short patterns, between 16 and 32 steps, and I set the sequencer to retrigger on every 4th step when I change pattern - this creates interesting dynamics in changing tracks and messing with scenes at the same time. You can create bridges, interludes and just jam session in the middle of songs and then go back to a more structured section of the song again.
So I use it as a sound design tool, but it’s also my choice of recording gear. Whatever I record, I do it straight from the Octatrack’s output.
Which is rather unfortunate, since I’m a pretty bad sound engineer and never get my mixes even half right.
But for those in the know, final mixes from the Octatrack sounds great 
