Basically it does the same as putting a script with llSetRemoteScriptAccessPin in the object's on_rez
Right now if you have a project that relies on updating scripts of rezzed objects, you'll need to make a script that sets the pin and requests an update via the llSay system. This makes said script a major failure point because llSay has a tendency of being dropped during lag spikes, forcing you to set up a syn/ack system. And if you later discover that your syn/ack system wasn't as robust as you thought, or want to change it in any way, you may potentially have hundreds of items that you need to manually rework.
Being able to set the remote script access pin directly on rez would eliminate the need for a syn/ack system entirely. Because you could:
  1. Rez object with pin
  2. Remote load the script(s) immediately in object_rez
  3. Profit!
Another added benefit of this system is that you could rez the object without the scripts that you intend to overwrite with remote loading, saving time rezzing the object.