Just to be clear, in case people dont understand why Pep plays inverted fullbacks.
Traditionally teams (and Pep has done this alot) tilt their back 4 over and have the fullback wide and winger inside. 4231 becoming a 3241 that Pep attacks in.
But this means when countered the fullback is far away from his position he occupies the winger spot, and has to run more distance.
But if you invert the fullback from a 4141 and still attack in the same 3241, if countered you have less distance to run back to. Its just less distance to cover while still attacking the same way he prefers.