This is why I keep two iPads. I didn’t go out and buy two at the same time to have two; I just kept my old one when I upgraded.
I still baby my M4 and my 2018 11” Pro is still good enough for the most part, so I’ll take the 2018 iPad to the bathroom, use it as I’m falling asleep, or anywhere that I’m worried I might somehow damage/scratch the M4.
Same here, I never buy 2 iPads at the same time, I just don't sell the old ones (sometimes I do, most of the time I don't). I like having 2 large pros so I kept the 2015 when I got the 2018, but then I sold the 2015 when I got the M1, now I got the M4 and I'll probably sell the 2018 soon and keep M1 and M4.
Spreading battery wear is not simply cutting it in half with 2 devices, you can cut it much more.
There was a study with shoes that showed that alternating 2 pair of shoes for 12 months (I don't remember the actual data) kept the shoes in much better shape that wearing each every day for 6 months running.
While iPads are different, you can cycle batteries much better and more comfortably with 2 iPads.
Sure some people don't know or care, to each their own. Others do. My 2018 11" pro battery is still at 95% after 4 years and over 500 cycles because I have taken care of it from the beginning. When I didn't take care in the past, battery were kind of shot by this time.
Also having a spare iPad for more risky situations can save you Apple Care+. I still use my 10.5 pro for when I do things in parks etc. where the iPad stays on the ground, grass etc.