I never saw a reason for it either. I'm almost always in a place with wifi. . . And then came 2017.
I was forced to upgrade to a new phone (a 7+) because my 6+ unceremoniously crashed. AT&T had a deal; buy an iphone, get the new LTE ipad for $99 plus two years of service. I did the math, and even with the two years of service, it was $339--far below the price of a new iPad at the time. I wasn't looking to upgrade; my Air 2 was working great, but I did.
And now I use the LTE all the time. It's mostly a convenience sake; I don't know that's really a necessity.
I find myself wanting a new iPad now. Not necessarily the latest model; I just want to use Apple Pencil. But I'm almost sure that I'm going to pay the extra $$ for LTE.