I agree with LABRat with his comments.
I personally bring 4. As mentioned in LABRat's post, many guys can average 200 with one ball. However, to regularly score more than 220, it will take carry, not just getting to the pocket. This is the reason to have options. Sometimes you want to change the entry angle to carry better or play a line that you're more comfortable with, etc.
I recently wrote this article on my site:
http://tamerbowling.com/index.php/what-does-your-ths-arsenal-look-like/Remember, having more options is not the key, it's knowing how and when to use those options. The article really focuses on making sure you understand your arsenal.
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