I have to respectfully disagree(about it not having much effect, not about it being repetitive because it definitely is) In previous versions I feel like it had zero impact, but in 13 I feel like it can make a big difference. Especially when you use the comment on head coach - pre match option. I pick something from "general comment about match" before every game I want to win (so I don't bother with the capital one cup).
The key is to picking the right option, you have to have a good sense for how strong your squad is playing right now and look at the opponent's match history and gauge how well they will be playing. Being cocky in the right situations (saying "He is dreaming if he thinks ___ can win this match, when you are heavily favored to win, should never result in a loss), can result in impressive victories, but you also have to respect your opponents enough. Sometimes it backfires for me, but I really feel like I have changed the outcomes of games just by using these options.
Another useful one is calling out opposing defenders as the weakest link. Especially if someone is injured or suspended and you know they have to use an untested prospect or something, if you call him out (but don't if he has high determination) you will often get the response that he can't get your comments out of his head and his morale will way down. If you set your passing to target where he is as well you can score a lot more than you should have. But this option is risky to use, only use it if you can clearly tell which defender is the weakest link, otherwise you may accidentally inspire him to prove you wrong and his morale will go way up.
But yeah, using the media probably isn't essential, I'm sure you can win every trophy in the game without it, but it definitely, definitely can help.