Does it help mpg, hurt mpg, or have no affect whatsoever on the Vue GL's performance?? I've been using it a lot more cause I think it helps heat up the cabin quicker, but may I'm an idiot for thinking that?

Anyone ever test this, or know for a fact which is better? Obviously you want it on if you got a tailpipe in your face, but otherwise, what's the general opinion for those who use their heater or air conditiong?

When I use the AC, I think it is better for mpg to run the recirculation so that the chilled air can be recycled back through the AC instead of taking in warm outside air.

When the defog or defrost is on, recirculation is disabled. The owner's manual has more information on this.

It probably helps (for the reasons SGL pointed out), but it won't allow the moisture in the air to evaporate and thus lead to foggy windows, forcing you to use the defrost, which disables recirc and runs the compressor.

We almost always use the vent/floor blend setting for heat, since it doesn't run the compressor, unless the windshield is really foggy. If there's just a little haze, I just turn the airflow to defrost but keep the fan switch off, since there's usually a very small flow of air at all times. That usually does the trick without running the compressor.