I live in a deer-infested area, my wife's cars have taken 3 deer hits in 12 years.
I'm not saying that's the primary reason [that would be the aforementioned looks and crushing another car]. But you asked what else other than that. What else would be the actual intended purpose of a bull bar (or "roo bar" as I have read they're called down under).
Your driving habits will show a greater or lesser effect on MPG than a simple 136 lb/61.8 kg addition to the vehicle.
Calculating the total front surface area of the bumper versus the stock bumper and expecting a change in MPG? Completely silly. It's like taking off your wristwatch and expecting your 100 yard dash run times to significantly improve. One would be better off removing the top, folding down the windshield, and driving that way for a decrease in frontal area and a measurable increase in mileage.
Just removing the air dam from the bottom of the stock front bumper will decrease gas milage by 1 to 1.5 mpg (and cause the hood to flutter at highway speeds). Wind resistance likely will have more of an effect on your fuel mileage than the weight. The main thing you will notice from weight with the stock suspension is more bottoming out while off road. These things already blow through the stock suspension travel on even small bumps. A bumper that adds 136 lbs right out on the front of the Jeep will cause that to be even more noticeable.
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