As far as I know, there are no advantages of using one mode over another, because you end up with the same result. All the tactic creator does is take the instructions you give, ie short passing, hard tackling, and the roles you give your players, ie deep lying playmaker and apply them to the players instructions appropriately. In other words, you can have identical tactics created in Classic mode or in the tactic creator. When designing tactics, I use both modes, I use the tactic creator to set up the basis of my tactic, then convert to classic to make all the little tweaks and changes I want.