In my experience it's always easier to give the team talk if you are playing badly/drawing/losing, I always go for the annoyed or disappointed options, you can almost guarantee a win.
Encouragement is a useful one when winning or drawing but it doesn't seem to work as well as the negative team talks. At the end of the game you can praise them for their effort/win so no harm done on the morale front. I had had plenty of player messages in the media about the manager's team talks resulting in the victory. When you are winning easily only encouragement seems to work, the rest of the time the losing team seems to come back.
Of course it could just be my teams, tactics, or the player characters !
Generally there is no praise at all until the end of the game, it doesn't matter what the half time score is ! | 
