Getting harnessed booster car seats is not only a smart decision, but some state's car seat laws also require it. Booster seats with harness are designed to keep your little one in place during bumpy rides. By restraining kids in harness, the crash's effects will less likely strike them, since this technology works towards protecting them as best as possible. During a collision, the movements are limited.  Any applied force will be spread into the booster seat, covering the kid's soft areas such as the abdomen.