If you need weights or not depends on TWO THINGS... And Two Things Only.....
#1 - Are you racing in a class (i.e. VTA) that has a minimum weight requirement.
#2 - Is your car "balanced"??
You may need weight to meet the "minimum weight" for the class, (I run a XRAY T2 '009... and I have to add A Lot Of Weight to meet the VTA Minimum).
You may need to add weight to balance your chassis. More weight on one side "verses" the other can cause handling problems.
U.S. Coast Guard (Retired)
Traxxas 4x4 (x2), Associated SC10,
XRay T3 '009 (VTA), XRay T3 '10 (USGT), Tamiya M05 (Mini),