Aside from the typical youtube/email/browsing/etc stuff that one does on any iPad, my iPad Pro is my laptop when I'm traveling for personal reasons (I bring a real laptop instead for work-related trips). After traveling with just an iPad Pro for so long, I hate when I have to bring a MBP now. Note that I have absolutely no need for the Pro version. I got it mainly because I really liked the display over the regular iPad.
I also sometimes use it as a guitar amp as there are quite a number of really good music apps for the iOS platform.
Gaming. Random browsing, reading books, watching movies, and so on.
Pretty much doing everything a phone can do except making phone call and sending text message.
Slide over is extremely handy, though I still wish free flow app window instead of either left or right position.
Browsing in bed before sleep. Checking email. As a big notepad for taking notes at meetings/conferences. Pull up recipes in the kitchen when cooking. Teaching students from scripted curriculum. Mastermind game.
I use mine in my living room when I'm watching TV for social media, games, email, and sometimes doing work. The terminal apps for the 12.9 are great, I don't have to leave my couch sometimes to get something important done. I'm not much of a gamer but I really like games on it when I do play. I also find it therapeutic to color with my pencil, so there's that. If I could VPN into my clients' networks then I'd be all set!
Edit to add:
I also like to play a movie when I'm doing something and then minimize it to a corner. That's probably my favorite feature of my iPad Pro.
IPP 12.9 - Web surfing, Reading (Kindle), watching movies ( Netflix / Amazon prime), access to iCloud docs, Apple Music / Spotify, use with Apple TV as a keyboard / remote, Password Manager Master, shopping lists reminders, reminder app for "to do's", Photos (great screen for viewing photos)
Also use Keynote and Goodreader extensively for work related sales presentations and sales documents - great to have a full size screen when presenting a product and showing pictures etc.
Treat the ipad as a media consumption/writer’s computer and some misc editing/Remote Desktop terminal device then you won’t have a problem using an ipad. For serious work, you’re better off with a real computer that has the horsepower to crunch numbers, editing video, streamline all sorts of “computer” related work.
The ipad is not meant to replace anything - but I use it for all media consumption, web browsing, writing, remoting into a desktop pc, social networking/FaceTime/duo conferencing, and mainly a long long battery life device for every day use. 90-99% of non-paid work is on this iPad Pro cellular model. The other 10-1% for paid work is on a laptop/desktop environment. But I end up taking my ipad everywhere with me for nearly everything (iPadOS) has really stepped up and made it worthwhile to own an iPad. Thank goodness for Jony Ive to leave apple - there is now hope!
Purely for work where I use Notability to take notes, write up development projects and tasks, and as a general scrapbook. Much better than pen & paper because they're available on all my devices. Hoping to use it as an additional screen for my iMac when Catalina comes out.
Comics. Lower end models don't have the storage capacities I want.
Typical consumption tasks. Some PDF markup and document review/comparison for work. On short recreational domestic trips, I skip the laptop and just bring the iPad (no keyboard). That covers the web browsing, etc. that I hate doing on the phone.
Study, research projects, writing papers, teaching from, presenting keynotes from, annotating PDF’s, teaching live online, creating and uploading videos, FaceTime, iMessage and FB Messenger, reading eBooks, emails and of course all the entertainment things. Having LTE makes not ever having to worry about finding WiFi a dream come true for working while I travel.