Personally, recording to MIDI is far more important than recording to audio, IMHO. It's one of my major beefs with newer Roland's (they dropped the MIDI Recorder).

It is cheap and easy to buy a simple pocket recorder (like a Zoom) and hook it up to your arranger wherever you go. But toting a full sequencer around in case you want to record the MIDI is FAR less practical (and, in truth, the timing is always better on internal sequencers than jacking everything out the MIDI port or USB into a computer). But here's why...

Who has EVER played something utterly perfectly? Who hasn't made the odd flub? Who hasn't listened back to an almost perfect performance and gone 'Damn! I wish the bass wasn't so loud, or I had less reverb on the piano'? Who hasn't gone 'This is great, but the second solo was on the wrong sound'?

With MIDI, all of these things are easily fixed, THEN you can record to audio. Of course, should you choose to record your performance warts and all, there's nothing to stop you from hooking up your recorder (or using one of the many audio recorder apps for your smartphone) and simply recording the performance as is.

But, with an audio recorder ONLY, all those options are gone, unless hooked up to a computer. Of course, ideally, the arranger should do BOTH. And many do. But if ONE got dropped, I'd prefer the audio recorder every day and twice on Sundays!