All of the above...!

The best thing about modern arrangers is there are no rules. You can use most of them as workstations, compositional tools, rehearsal tools, and live performance instruments in any situation from a full band to a solo performance.

You are kind of asking 'What can you do with a guitar?!'....... The answer is 'Anything you want to......'
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An arranger is just a tool. What matters is what you build with it..!