One of the reasons you buy a Nexus device is easy, complete access to the device hardware. The stock software is great, but we all know sometimes its fun to tinker around with your own creations. Nexus devices have locked bootloaders out of the box (and that's a good thing), but unlocking them is trivial. Just like the Nexus phones and tablets before it, the Nexus 10 is no exception.
Just because unlocking the bootloader is easy doesn't mean it's for everyone, however. Part of unlocking is understanding the risks that come along with it. Having a device running with an unlocked bootloader means that anyone who has access to your device in turn has access to every bit of software (and personal data) on it -- even if you're using security measures such as a lockscreen.
If you decide that unlocking the bootloader is something you want to accomplish, then doing it right out of the box is a good idea. The process of unlocking completely wipes all of your personal data off of the device, so you won't want to do this two months after you get it. You'll want to spend the little bit of time to unlock first before setting it up just how you like it.
Alright, now that we've got that out of the way, let's double up unlock your shiny new Nexus 10's bootloader.