Hi yngerman1.
Original JDL would complement Shomrim by taking things to a higher level of protection.
For starters, JDL would create a deterrence by a strong presence of individuals who would go into high risk areas on foot patrol. These individuals would be skilled, capable, and inclined to engage in self defense. This would be much like what is now taught in anti-bullying classes; strong presence and ability to physically defend. Such a presence is proven to work against criminals who are prone to, c”vs, assault, vandalism, mugging, theft, and burglary.
I liken their role similar to what we think of today with the Guardian Angels.