This option in DSMLink is provided for users running a non-factory airflow metering device that does not need varying intake or barometric pressure signals. Typically this would be a GM MAF used with a GM MAF translator.
A factory Mitsubishi airflow meter works by measuring temperature, pressure, and volumetric airflow data and sending all three pieces of information to the ECU which then calculates the mass airflow value. Note that the metering device only measures temperature, pressure and volumetric data. The ECU then calculates the mass airflow value from these three pieces of data. Mass airflow is the important value here, not volume, for calculating fuel demand.
So when running with a factory Mitsubishi airflow meter, the ECU must see all three signals from this sensor. When running something like a GM MAF with a MAF translator (MAFT), however, it does not. That's because the GM MAF measures mass airflow directly. The translator's job, then, is to take this mass airflow data produced by the GM MAF and send it to the Mitsubishi ECU in some way that the ECU code can end up calculating the same mass value as the GM MAF originally indicated. The translator does this by holding the temperature and pressure inputs to the ECU at a constant, known value and then varying the volumetric signal. The result, inside the ECU, is a mass airflow calculation that ends up producing the right value. But only because the MAF translator was holding the temperature and pressure signals at known values (around 80F and sealevel pressure).
So, if you can clamp the temperature and pressure signals inside the ECU with software while running a GM MAF with MAFT translator, then those physical inputs to the ECU become available for datalogging other sensors instead. That's the primary purpose of the Ignore IAT/Baro option. But take note of the specific conditions under which this option can be used. It can NOT be used when running a factory Mitsubishi airflow sensor because all three airflow signals are required by the ECU.