As i said in another thread of Abhi, in real football at this period there is no zonal or man-to-man
Older times it was m-t-m
Then zonal
Then a combination of two
zonal & man-to-man of the best defender to the key-player of oppo (Marandona).
Now it's the triangles.
When the attacker has the ball, he is surrounded from a triangle of defenders.
About the game :
man-to-man seems to give a little advantage in defense (but not sure)
and gives an extra condition loss (for sure).
So I don't use it at all, unless for emergency situations
(last minutes of a critical game, to keep the score, if I remember to do it, haha)