Sway bars stop your vehicle from leaning, typically in corners at speed, generally on a surface where traction is good, the body would tend to roll or sway the most. This benefit is, for the most part, valuable on-road. Certain types of off-road specific builds remove them completely. Others use, as mentioned earlier, disconnects.

Having no sway bar, disconnects, or an actuated sway bar removes some of the travel limitations of the suspension (ie makes it easier to travel through the stroke), giving you more tire to ground contact in offset terrain. It is easily possible to go faster in this circumstance and not be getting the full benefit of your suspension. 12mph is not that fast, particularly if you are accustomed to driving the terrain.