Do I want SIM security enabled or disabled?.....

My Storm is unlocked and the SIM card is registered. I did that for no particular reason as I have no international travel planned - I just got caught up in the "call Verizon and get your unlock code" fever a week or so ago.
So, here is my question: What is the "Security enabled/disabled" option about? Given that I am using the Storm exclusively in the USA, which option do I want in effect? Also, to "Enable" requires a password - is it just my PIN? What does the (3 left) refer to in the Password field when trying to enable?
Thanks!

You do not need your SIM pin enabled. This is only if you move the SIM from phone to phone or if you want to type in your SIM pin before using the SIM in this phone. The device password would supply you with ample security.

it's my first experience with a SIM card. If I'm travelling, will the GSM work regardless of security setting (Enabled or disabled)? What is my SIM PIN - is it the phone PIN or do I have another PIN I am unaware of?
Thanks for laying out the VERY basics!