Moto X - Unlocked or Locked Bootloader, what is the difference?
Locked vs Unlocked Bootloader.
If your phone has a locked bootloader, you are restricted by the phone and its security measures. You may only flash components (recovery partition, system partition, modem files, etc) or entire roms/sbf files which are digitally signed by the phone maker, in this case, Motorola.
Having an unlocked bootloader means you are free to flash any component you want, be it from Motorola, or a 3rd party developer.
What difference does it make?
Well, if you want to ensure you can root, you want an unlocked bootloader. If you want to be able to run a 3rd party custom rom, like CM, or such, you must have an unlocked bootloader.
Ok, so what effect does Locked vs Unlocked boot loader have on Rooting?
If you want usable root on the X you need two parts 1. Root Exploit, and 2. An Exploit that allows for disabling Write Protection.
If you have a locked bootloader you need someone to find these exploits and create a process to use them to gain root and disabling write protection. You basically need to find and exploit a flaw or vulnerability in the phone, or its software. i.e. Hack It.
When Write Protection is enabled (the phone's default state with locked bootloader, or the state you are in after you install 4.4.2), any changes made to /system, or the like, (including, but not limited to, App installs, file modifications, deletions, renames, etc) are not permanent and are lost at power off/on.
Even if you have root, but lost Write Protection, any apps you've installed that need to write to system can't permanently save their changes (you have to re-do every time your phone powers off/on), and any Root type app, or app that gets installed to /system after WP is enabled will be lost at power off/on.
As you can see, Root is only half of the equation. For root to be useful, you need to be able to write to /system, in the X's case, this means you also need write protection disabled.
For Android 4.4 or lower on an X with a Locked Bootloader, Root is done via SlapMyMoto exploit/process, and write protection is disabled via the MotoWpNoMo process. They rely on downgrading and taking advantage of vulnerabilities which existed in the 4.2.2 ROM. If you've used these processes, and then take the 4.4.2 OTA update, you'll usually keep root, but will lose Write Protection Disable which MotoWpNoMo gave us.
The 4.4.2 ROM and update patches the exploits used by SlapMyMoto and MotoWpNoMo.
Another concern with 4.4.2 are that parts of that version 4.4.2 updates (like bootloader, gpt.bin and such) now prevent successful downgrading of the rom/bootloader which the SlapMyMoto and MotoWpNoMo processes relied on. If you try to downgrade from 4.4.2 to 4.4 or lower, you could BRICK your phone (for more see DOWNGRADE). This is another reason why SlapMyMoto and MotoWpNoMo can't be used if you have 4.4.2 on your phone already.
JCASE has now released Pie for Motorola phones with locked bootloaders. While it Roots 4.4.2, it doesn't disable Write Protection and there is no way to disable write protection if you have a locked bootloader. Because write protection is still enabled, this root process does not survive power off/on and root type apps can't write to /system and the like.
Pie for Motorola doesn't work to root 4.4.3 because the exploit used is already patched in 4.4.3.
Safestrap works today to run rooted 4.4.2, but you have to root and disable write protection first. So IF your X has a locked bootloader and is on 4.4 or below, you can root with SlapMyMoto/MotoWpNoMo, then use Safestrap to run a rooted 4.4.2 as an option. But there is no promise or guarantee that future ROM updates will be compatible with Safestrap, and if you need a replacement X and it has a locked bootloader and comes with 4.4.2 on it, you wont be able to root it to use safestrap.
As time goes on, finding vulnerabilities to exploit to gain root and disable write protection on a locked bootloader phone are becoming more difficult. With a locked bootloader, you need to rely on someone finding them and using them to create repeatable processes for the end user community to follow in order to root and disable write protection on their phones. There is no telling how long this could take. It could be days, weeks, or even never.
BUT... If you have an unlockable bootloader, no exploits are needed. Unlocking the bootloader disables write protection and allows you to flash unsigned components (like 3rd party recovery, non-Motorola ROMs, etc). This also makes root easy (just flash a 3rd party recovery, boot to it, and install SuperSU from there to root). This is not impacted by changes Motorola might make in the ROM and bootloader code, or Google might make to Android itself. You can take future updates and still be able to root and have write protection disabled. This is why the Developer Edition and bootloader unlockable phones are so attractive.
So having an unlocked bootloader, or at least having the ability to unlock the bootloader when you're ready to root, is the only way to ensure you can always root and disable write protection.
Motorola freely gives out bootloader unlock codes for the Developer Edition phones, as well as some carrier editions (but not ATT, Verizon or Republic Wireless Retail/Moto Maker editions). Requesting the code for Non-Developer Edition models does void their warranty.
When it comes to unlocking the bootloader of the non-Developer Edition Verizon, ATT Moto X and Republic Wireless X, the only way to do it, is via this 3rd party unlock solution, which is why there is such a buzz about this, and many people paying to get a code for their phone. NOTE: as of April 1 this 3rd party option was longer available. Recently it has returned see the thread -> China Middleman Back??? there is always a chance it will go away again.