[RC-Monster Mike]

As mentioned, droop is the amount of down travel the suspension has. Not affected by battery weight, but here are some key handling impacts this adjustment can have:

Limited droop will effectively limit chassis roll(which generally lowers traction) - an example where this would be effective would be a smooth or hard packed track where you have lots of traction and wish to minimize chassis roll for quicker transitional handling and less possibility to traction roll the vehicle, as well as lower overall traction to allow you to slide the car a bit better. Stiffer sway bar springs, shock oil and shock springs would impact handling similarly from a traction perspective.
Conversely, a setup with lots of down travel is best for rougher tracks, lower traction tracks and large jumps. More down travel allows the shock more time to absorb a large jump, allows more overall suspension movement(increases traction and chassis roll). A softer sway bar, softer shock oil(except for big jumps of course) and softer shock springs will impact handling similarly.
:)