Coercivity is the resistance of the particles to a change in position. Higher coercivity is necessary for higher capacity tapes because the magnetic forces between the increasingly densely packed bits increase, causing their individual signal strength to become weak and blurred. BaFe and similar compounds are oxides and therefore less susceptible to the demagnetization that can occur between closely spaced particles. This ensures that not only is the data stored with a low and reliable error rate, but also that once it is recorded, it is stored exactly as it was captured.
BaFe media has better magnetic properties compared to MP media, resulting in better signal-to-noise ratio and bit error rate.
This will play a role from LTO-7 onwards, but is currently not relevant for LTO-6. Tests by HP found no discernible difference between MP and BaFe.