It isn't just to stay clean, it needs to measure the true inlet pressure, taking account of any pressure drop caused by the filter and calculate the optimum fuel/air ratio.

 

But what relevance is knowing the pressure right at the beginning of the intake system when you then have numerous other pressure drops along the way such as intercooler and intake resonator which are closer to the engine? And then you have the turbocharger constantly changing the intake pressure by magnitudes more than the small restriction the airfilter makes and this is the pressure closest to the engine which the engine actually sees. So im unsure what relevance this initial inlet pressure is when the actual pressure the engine receives is different

 

If anyone actually knows the purpose I'd appreciate it, thanks

 

There's plenty of info on the Web, if you want to trawl through it. I haven't come across anything that contradicts what I've already said. Suffice to say that this sensor is just one of many used by the ECU to accurately compute fuel/air ratios, turbo and EGR operation, etc., for maximum engine efficiency and minimum emissions. The details of how all this is achieved will be in the ECU software, but I wouldn't expect it to be in the public domain.