No you dont need to use OI and you dont need to teamtalk at all.
But then dont expect to win to many games neighter :/
If yo uwant to win you need to take countermessures for everything, and never ever ever go for the "GJ GUYS" teamtalk if you are in the lead at halftime. i jsut lost 7-2 to Inter and ragequit after beeing up 2-0 at half time telling the team i was you did good, but you can do better xD
Getting tired makes you sloppy, and to win you need to be the manager.
Opponent change formation and bring on a pacy winger with low bravery? Tight mark his *** and stick on hard tackling and he wount even go near you're defenders.
small things like that.
But i do belive the team talk system does not work as intended, as encouraging the team to boost their morale when they are playing ok away from home should not resoult in a 7-0 loss in a 2nd half.
you just need to play a lot to find out what works, and in general i ALWAYS use assertive teamtalk, and passionate if in a derby etc.
If im up at halftime i use Calm or assertive and tell the guys to not get complacent.
its a struggle before the patching is done like always
Welcome january i say!