I don't care for the fact that you have to make transactions the day before in order for them to take effect for the next day's game.
I don't have a problem with Yahoo not allowing managers to add players on game day. It makes your bench a lot more relevant. You can still change your starting lineup right up until the first pitch of each game.
Now, ESPN only lets you make changes to your starting lineup the day before each game. That's a hassle if you're going to be out of town or too busy to check on your team, or if a player gets hurt in a late game and you don't find out about it until the following morning.