Grille Guards have become a very popular truck accessory, not only because they look good, but also because they have a real function on trucks that see heavy use in business or off-roading. Grille Guards should only be mounted on vehicles featuring a separate frame, and be mounted directly to the frame. On uni body cars, or passenger cars with carefully designed deformation zones, airbag sensors etc, they do more harm than good.
Properly designed, properly built and properly mounted grille guards offer very good protection for a car grille in collisions with animals up to about the size of a deer, in parking lot collisions or when plowing through brush in off-road driving. They do not offer any extra protection in serious accidents. If you hit a big animal, you and your vehicle risk serious damage whether you have a grille guard mounted or not. The grille guard can in some types of accidents make matters worse, as a very sturdy grille guard is stiffer than a car body, making the stop more abrupt and violent than if unprotected body panels are allowed to crumble. Grille guards can also cause aggravated injuries if your vehicle happens to collide with an unprotected person. This is also why some countries have banned grille guards. Used in their proper context, and on vehicles where they can be properly mounted, grille guards can be almost indispensable. It is no coincidence that you find grille guards on most light trucks used on farms or in the construction industry. The grille guards are very valuable in rough or crowded environments where low speed hits are common.
A front guard that covers both the area in front of the radiator and the vulnerable headlights can save both money and trouble for off-road drivers. It protects the front from being scratched when the vehicle is driven through bushy terrain, and it prevents damage by stones and debris thrown up by other vehicles. A front guard built to accept a winch does double duty, providing an excellent mounting point for the winch, while at the same time protecting the vehicle from stones and debris that can be thrown up by assisted vehicles that spin their wheels trying to get out of a rut, and protecting sensitive and expensive-to-repair parts as the radiator and the lights in case the wire rope snaps. A punctured radiator can get you stuck in the middle of nowhere, which is why grille guards with mesh inserts are popular with off-road drivers. Front guards also provide a perfect mounting point for auxiliary lights. The raised mounting point gives the lights a wider range and provides better visibility than if the lights are mounted directly on the bumper. Utility style front guards often feature rubber clad push bars that can be very useful when assisting other vehicles, both on and off the road. If a vehicle stalls on the freeway during rush hour, it is nice to be able to help it get onto the shoulder without anyone risking his life by stepping into the traffic.
The protective value of small chrome bars protruding under the bumper is debatable, but there is no denying that they look good and that they provide an excellent mount for auxiliary lights. Just don't expect these decorative "bull bars" to protect your vehicle from damage in case you collide with a bull.