Focusable LED lights typically use a fresnel lens to enable the beam angle to be adjusted. The fresnel lens can be moved closer and further away from the light source, which changes the focus angle of the light. Adjusting the beam to a narrow angle provides an intense "spot" of light. A spot is often used to create some variability in the background, to provide separation of the main subject from the background, or to highlight a part of the scene. Broadening the angle provides an even "flood" of light to bring up the exposure of the shoot.
LED fresnel lights are increasingly replacing HMI and Halogen "hot lights". The power consumption of an LED light with a similar light output is around 80% less than that of a Halogen light. Aside from using much less power, another key benefit is LED has much less heat output, providing futher cost savings on air conditioing in the studio. An LED chipset has a lifespan of 30000 hours, meaning you dont need to factor the cost of replacement globes into the total cost of ownership.