The following is an excerpt from a pretty good article on etrailer.com that might help. Its worth a read.
When you're towing a trailer with a standard rear-mounted hitch, your trailer's tongue weight is transferred to the rear axle of your tow vehicle. As a result, the back end of the vehicle may be forced lower and the front end raised. If this happens, your vehicle's rear axle will bear the weight of not only the trailer, but much of your tow vehicle's weight as well. Less weight on the front axle of your vehicle can cause diminished performance in terms of steering, traction and stopping power. It can also increase trailer sway. And your view of the road may be limited due to the awkward angle.
Weight distribution systems use spring bars to help combat the problems that often occur with standard hitch systems. Adding spring bars to your towing setup applies leverage to either side of your system, which transfers the load that is pushing down on the rear of your vehicle to all of the axles on both your tow vehicle and your trailer. This even distribution of weight results in a smooth, level ride, as well as the ability to tow at the maximum capacity of your hitch.
2016 Jayflight 26BHS Elite
2014 F150 4x4 Super Crew, Eco-Boost, Max Tow
Bayliner Trophy 2002ff