This has been discussed quite a bit => Activate cellular on my new iPad Pro?
To answer your question, I still have LTE activated on my iPad even though my phone can tether. Tethering is simply not as smooth/easy as turning on a cell antenna on the iPad. Also you don’t have to pay a month fee per se. I use TMobile for my iPad (iPhone is on VZW) - inpay $10 for 5GB which lasts 5 months. A killer deal for the way I use my iPad. For super heavy portable use, I can also see the benefits of just adding it to the plan for $10/mo. YMMV