My theory is that it's better to have more players on the defensive side of the field plus zonal mark. I believe that man-to-man makes always battles 1-on-1, so the opposition will have 50% chance of winning these battles.

I use man-to-man when i play formations that leaves some open spaces in my defense, like 41212ND leaves flanks open.
It has been working fine, but it's just a theory hehe