Traction bars help prevent axle wrap. Which can lead to wheel hop. Also when launching on the track energy used to forward motion the truck will be lost in teh twisting of the axle. And its reversed energy will be released slower rate then which it initially applied (another words, you wont gain the energy back going down the track).
However with a traction bar pushing the load toward the front of truck it may stop axle wrap, but it could cause axle to 'roll" back with the axle rotation. On 99% of street driven/weekend race trucks, a set of cal tracks or traction bars will be just fine. Your ultimate would be a 4 link preventing any axle wrap or add a reversed biscuit bar over the center of the axle along with traction bars.....
here is a pic of my bars.
