They're the best way to do things, so long as it's used properly. You can't veto just because you don't like a manager, or his team being improved. If a trade is fair, then it's fair. If there's collusion, then people can veto it. And it's pretty obvious when things get to be collusion. If 8 out of 12 teams think it's absolutely not a fair deal, then it should be veto'd, honestly.
Say in fantasy hockey, I try to trade a goalie - say Connor Helleybuck for Sidney Crosby. I have two great goalies already, and want to move my third good goalie for some offensive help. And I do it because the guy who has Sid has a terrible goalie group. That's not collusion, but I would expect that trade to be veto'd, and rightly so, because it's just not fair or right. I'm not one to sit and watch someone take advantage of someone else. Offer up a fair trade, or get it veto'd. You offer up trash, then you should expect it to be veto'd. Lopsided trades aren't right, even if they're not collusion.