VFLs work well for exposed lengths of fiber near a patch panel by illuminating bad connections and breaks. They are not very helpful for cable runs more than a few meters, or when the cable not visible or accessible, or when the laser light can’t penetrate the jacket.
Optical Time Domain Reflectometers (OTDR) provides graphical data and analysis along the entire length of a cable, way beyond the reach of a VFL, but they can be expensive and require more time to and skill to operate.
Fiber QuickMap fills the gap between a VFL and an OTDR. These models have the simplicity of a VFL, and provide distance and power information on high losses, breaks, and the end of the fiber.