12v Motor Control

As you know I'm new to the Arduino (and electrical stuff) and I do not understand the data sheet completely.

  1. When it says the "typical voltage loss" does that mean that I can rely on the fact that it will typically be that much lower or are their test results not practical when it come to real applications?

  2. What exactly is voltage loss. I know that it means you lose voltage, but when do you lose it? Do you lose it when power goes into the shield, and can combat that with a bigger battery, or can you combat voltage loss with a good program?

Thanks for all of your help,
Drew Davis