Irrlicht Engine

I'm new to Irrlicht and creating games in a 3D space. I have a few questions.

1) Do most people (I'm talking in a non-professional setting) find it worthwhile to create a world editor for their game no matter the size?

2) As for pathfinding I understand the concept I'm just not 100% certain how ...

If you know that performing

action A + action B = C

You can reduce network traffic by transmitting only what is necessary. In the context of a game consider this:

The game knows where Player A and Player B are standing. Player A knocks back player B and sends him flying 3 units while Player A is ...