If you say these last few words, 'self assessment simplified system', loudly and quickly a discernable 'hissing' can be heard, similar to that emanating from many tax practices as one passes by!
Although there may be many reasons for such 'hissing' (FSRA, GST, FBT, CGT discounts and rollovers) its most probable cause is related to tax assessments, amended assessments, Part IVA determinations, penalties, GIC, ATO IDs, debt resolving, and the biggest 'hiss' of all - preparing for a challenge with the ATO.