What does import key do?
 

A while back, when following some tutorial to build a Centos 5.3 server, I came across the following:What does it do? Is it required for Centos 6.4?

Thank you

As far as I know (and can tell) it imports signing keys to ensure you're not stuck with messy stuff (virusses, trojans other stuff) in the repo...

Thanks Thor,

So this was specific to a given repository, and I would only do such a thing when using that specific repository?

As far as I can tell yes...it's just about the same with Arch Linux, the command there is pacman-key...but the general idea is the same: security...

yes many repos have signed PGP keys, that is exactly what you are importing. when you run yum vs that repo it will verify that the PGP key you have matches that of the repo's URL. this is for security and safety.