mobile

Hi there,
Sorry to say that I'm sure this has been asked before, but I couldn't find the right search query to find a decent answer.
I'm curious what the value of a sim unlock from one of the many websites out there is? I don't mean the price, but will that code alone make my phone usable in a different region (assuming that the network type is supported?)

I've read a lot of information about region locks on phones, as well as SIM locks. I guess to simplify my question: Do I need to do both of these things, or is the SIM unlock sufficient?

Thanks so much to anyone who can help or direct me to a decent answer.