First off... The pan was tapped with a second hole for the sensor
. That tapped hole is the black plug in the center of the picture. I don't know how you would used the drain plug hole for both a sensor and a drain. The drain plug was the big plus in this for me and I would not want to loose that functionality. The hole for the temp sensor was an added bonus and worth the additional $40. (I am not brave or stupid enough to drill and tap aluminum with the tools that I have.)
Benefit of extra fluid?
Just like additional oil helps an engine, additional ATF helps a transmission. It helps handle heat.
Does the trans run cooler?
IIRC-Their website says that you can expect a 10-15 degree F drop in trans temps. I have noticed that the transmission stays out of overdrive longer on colder mornings. It takes 2-3 miles longer to reach operating temp when outside temps are below freezing.
Is there risk of ground contact?
Yes that is always a possibility but not likely for me. I also have slightly larger tires on the WJ so I picked up some addition height there. If that is a concern then one of the other pans (that holds more fluid) is available and it fits under the factory transfer case skid plate. I would say this one is .5" deeper on one side and 1" deeper on the other. The major difference is that the stock pan was a step type more like this PML pan: YourCovers.com Dodge RFE Transmission Pan, Low Profile, with Clearance for Exhaust and Frame Cross Members
Check out this vid. It talks about the stepped pan #11078.
Here is a CRD Liberty install. This is the same pan that I used and addresses your concerns about clearance.
Jeep Liberty CRD transmission deep pan