I always found this view interesting, and many do share your opinion. For me it's the other way around - I had a cellular iPad Pro 1st gen and never used it (the cellular, not the iPad), and thus my 2nd and 3rd gen iPad Pros are wifi only. If I'm home or in the office, I have wifi and when I'm outside, on the street - I'm not going to pull out a 12.9" iPad to surf or check email. And, if I'm somewhere where I really need to use my iPad and there is no wifi, thanks to tha few taps connects the iPad to my iPhone's hotspot. So I really don't see the benefit. Where do you use your cellular connection with your iPad?
Well we can agree that a 12.9in ipad is not best suited for LTE. I have the same ipad, it doesn't have LTE and it's fine. Things are difference for a standard size ipad or an ipad mini (I have both, and both with LTE)
There are several points to consider with LTE:
1. Sounds obvious, but you need a dedicated SIM card. Some people find it crazy to spend more money but it really depends on what your carrier offers. I have an unlimited plan and for just $10 a month I can have a dedicated 2nd SIM to share the plan. For me it makes sense.
2. At home it can be useful if your ADSL / Fiber etc. has interruptions. It has happened to me, fortunately not often and in this case it's great not to have to rely only on your smartphone. However let's say that this is secondary, not a reason by itself.
3. I work at different locations, at most of them I have Wifi, but at one of them, twice per week, I don't.
4. On business trips / holiday (I have 4GB of roaming in my plan), LTE is essential in my opinion. If you travel once a year it may not make sense, but I tend to travel every month or every 2 months, between work and holidays.
5. On the street.... Well, I think here it's more a matter of what person you are... Are you someone that does most things of their smartphones? In that case, even bringing an ipad makes little sense. I tend to use my smartphones only for notifications, calls and photos. I hate writing on glass. I feel the need for a true keyboard for anything that is more than 5 words... unless I have no choice...
Also, multitasking is hard on a smartphone and much better on an ipad. Typical example: waiting at the doctor, dentist, etc., queuing, waiting for someone in general... If you are sitting you can do a lot of things with a keyboard and even if you are standing you can multitask quite a lot more with an ipad than with your smartphone....
By the way, yesterday, while working at the location where I don't have wifi, I tested using my Iphone SE as a dedicated modem. It worked perfectly. Problem is, I may forget to charge it since I rarely use it, contrary to my ipad... So I need to to always have a power bank with me just in case, 2 additional (small) things to carry... Having said that, the big advantage of the new ipad pros, is that they can charge your phone... So they make lack of LTE less of an issue if you have a dedicated smartphone/modem laying around... Again not a perfect solution, but it has the advantage of the additional freedom to choose which ipad or even laptop to carry with you if you have multiple devices