Simple. To see if the prospective candidate can really fly an aeroplane
Jetstar candidate simulator tests were done at the Qantas simulator facility at Melbourne. Prior to that, the Ansett Aviation Training Centre 737-300 Level D simulator was used. The assessment test is conducted without the aid of flight director and autothrottles. The speed was kept back to 180 knots for all manoeuvres except on final for an NDB and an ILS.
The test included a take off and climb to 4000 ft, basic instrument flying skills with steep turns, set rates of climb and descent at fixed airspeed, and basic asymmetric handling in level flight. No checklists. The actual landing from the Cat 1 ILS was not assessed as it was felt it was unfair to throw a candidate into the deep end of a jet transport landing/reverse thrust etc without previous dual instruction. At some point during the assessment the candidate was required to demonstrate navigational situational awareness by fixing the current position by means of purely ADF cross bearings.
There are some turbo-prop operators who for cost reasons prefer to assess their candidates on a generic 737 NG Microsoft flight experience synthetic trainer. These are located in some capital cities to attract tourists. Certainly cheaper than a proper Level D full flight simulator but lacking the fidelity. These operators may require the candidate to learn off by heart a whole series of generic checklists and mandatory call-outs as important to the assessment. On the other hand the Jetstar thinking is the assessment should be on purely on general handling ability, and instrument flying skill - without the additional impost of requiring the candidate to learn a generic checklist during the 30 minute pre-flight briefing.