There's another aspect to the spring thingy. If the front end is loaded with panniers or especially a handlebar bag so that the weight is forward of the steering axis it will tend to destabilise the steering. This occurs because the weight acts as a positive feedback loop by exaggerating wheel flop. Some touring bikes are built with zero or near zero trail to combat this but that can make them iffy to steer when unloaded: flop follows trail so if you eliminate one you eliminate the other. Trail acts as negative feedback on steering deviations and stabilises the front end.

The right amount of tension in the centreing spring will counteract the wheel flop and allow the use of a normal fork rake and hence trail with a weighted front end.