Only the cellular model has an actual GPS chip.
I find the cellular data is most useful when I go on a trip/vacation.
It is wonderful not having to hunt for WiFi.
I also find that when I'm traveling I run down the battery on my iPhone faster than usual so having my iPad online keeps my iPhone juiced up for when I really need it.
Even if you use it only 2-3 months a year, you will be so happy you have that feature.