I took mine off and have not noticed any cons from doing so.

 

A lot more hood flutter. Until I got the daystar hood wranglers.

 

The purpose of the JK air dam, (so named by Jeep), is to direct air under the front end.
In doing so, it reduces drag, and lowers the pressure in the engine bay.

Some people who have removed it have reported a slight decrease in gas mileage, and an increase in hood lift when trucks go by in the opposite direction.
The increased hood lift indicates an increase in pressure under the hood, which means there will be less air going through the grill and radiator. That won't be a problem until you are operating the Jeep at the upper limit of its cooling capacity. An automatic transmission is likely to be the first to suffer, especially with the pre-2012 JKs not running an aux cooler.

A metal skid plate under the bumper will do most of what the air dam was designed to do, plus give a lot more protection.

 

So in effect, would removing the air dam while having a vented hood help with cooling ? I mean it seems with the higher pressure under the hood, with the vents or a louver it should help with drawing more air through the engine bay, therefore assisting in evacuating the hot air, in turn helping with cooling.
Just me thinking out of the box.

 

An air dam forces air around the vehicle. Keeps vehicles more stable at higher speeds and is also used to shape air flow to the radiator, for cooling the brakes and any other possible components (ie...transmission or power steering coolers).

An air splitter forces the air to go under or over the vehicle. By doing so, it allows for more or less down force depending upon setup.

 

Odd.

I thought the only purpose of the: air dam, front bumper, blocker beam was to provide job security to the garbage dudes.

My mistake.