Strange that, as Turbo Technics recommend it as recently fitted one on mine, and also most manufacturer's i've worked for recommend it as good practice also replacing the feed pipe/fitting a filter (or cleaning if already fitted) before doing this.

That's why they recommend doing it post turbo (on return pipe) as that tell's you it has oil feed and that there's no problem with the turbo itself, oil pressure gauge is waste of time as it's dictated by the engine and if the oil pipe is new or filter cleaned it's just wasted time IMO.