Advice? New T5 lighting

Just picked up a T5 lighting fixtures. Just a couple questions is there a reason I can connect 2 black and two white wires? I know a little about electrical bit cannot think of a reason whyou I would need more than one black and one white input wires.

Also any idea that this other piece is for? (See pics)

 

Dim option would be my bet. I would just hook them up in series you should be fine.

 

I asked an electrician and I was told it was for a larger current than we have here in the states. So I only need to use two of the holes. Any thoughts on the other tie fighter looking piece. What is that for?

 

When lighting is installed in a commercial application with a drop ceiling, armored cable with the wires preinstalled is often used. They have cable connectors that snap onto the end of the armored cable and then snap into that piece that would be installed in the housing where the electrical enters instead of using conventional conduit connectors that fit in a standard knockout hole.