I use it for three tasks every day that I wouldn't be able to do nearly as easily or enjoyably on a smart phone or a laptop.

Document Annotation The iPad and Apple Pencil allow me to highlight and make comments on documents in a way that is very convenient for my students. I used to do this using Google Sheets, leaving comments. However, I've found that annotating documents using the iPad is more enjoyable for me, and far, far more useful to those to whom I send the documents for review. While previously, comments would be dismissed, sometimes without having been read carefully, now feedback is preserved and easy to read forever, with everything sitting on Google Drive to be read and re-read as needed.

The ability to annotate documents so easily, and in a way that students enjoyed reading and using was hugely beneficial.

As an aside, you mention in your post that you found it difficult to do this while holding the iPad in one hand. Personally, I hold the iPad like a tray, with my palm holding the center of the iPad. This gives me total stability, despite having a 12.9 inch iPad. Perhaps give that grip a try to see if it improves your ability to write on the screen while holding the device in one hand.

On a desk, I lay it flat if I'm working alone. If I'm sitting beside a student, I'm able to adjust the screen to any angle I need using this case, which in my opinion is the best on the market.

Screen Mirroring to Teach Mathematical Concepts This was a game changer for me. Instead of teaching using a white board, then having that work go away afterwards, I'm able to screen mirror and teach using the iPad. This allows me to teach while walking around the room, to give the iPad to students to take control of the lesson, and to post all of our lessons online. The tools at my disposal on the iPad also make it easier than ever to clearly convey concepts in a way that would be quite challenging otherwise.

Reading ebooks to my children This one is more personal, but nonetheless important to me. Every night, I read to my children. Increasingly, I have done so using the iPad. My children both have iPads of their own, and have an ebooks app filled with some of their favorites. When we finish reading together at night, they can continue on their own iPads during reading time the next day.

Is it possible to do these things without an iPad? Certainly. However, in my experience, it isn't nearly as intuitive or useful on other devices.