Income Tax Assessment Act 1997
You need not record an income-producing activity. But if you don't, the activity cannot be taken into account in working out the extent to which you can deduct an expense you incur for the travel.
If you fly to Los Angeles for the sole purpose of attending a 7 day conference, but you don't record the conference in your travel record, you cannot deduct the cost of the air fare. This is so even if you have written evidence that you paid the fare (eg a receipt), as required by Subdivision 900-E .
You don't need to record any other kind of activity, although you may do so.