LDraw.org allows third party part in the LDraw Parts Library

[Philippe Hurbain]

I don't know what to think of this. I mean, what's the use of this? I can't think of any 'widely' used unofficial part besides the sBrick.

To name a few:
- Hitechnic and Mindsensors Mindstorms sensors and actuators
- Firgelli motorized linear actuator (Mindstorms)
- Rotacaster omniwheel
- Brickarms/Brickforge/Brickwarriors minifig accessories (and probably many other!!!)
- Big Ben train stuff

And the L in LDraw stands for Lego right?

Exactly. "for LEGO"

What's the use of making third party parts 'official'?

To get something reliable for this kind of stuff, to have one centralized placed for LDraw parts.