I mean really, why would you ?
As it turns out, they really help. Free typing games help you to improve accuracy and speed. If you want to start typing faster - this is kinda the best way to start.
Well, it is a nice way to kill some spare too. Funny way I should say. Basically, you are improving your typing skills simply by having fun. Even though you think that you type fast enough, you can try and see that in a few hours you really start typing faster.
Here are the best typing games of all times:
QWERTY Warriors 2 - This is kinda the best game on the net. It's professionally done and looks great. It's very to play this one also.
Ghost Attack - Another great example of how the games should be done. It's pretty simple, yet very effective.
Anyway, you should try both of them and then explore this blog, I've done my best to collect the best games from the web.