I always do if possible. Just because some of the new features that some devices have, I might not be familiar with, so I like to familiarize myself with how it works. Since electronics are expensive if you like a lot of devices, I want to make sure the features are something I would want and work for what I need in my workflow. I have a 27" IMac, but tried that before buying, mostly because it was a very expensive purchase. Even though my buddy's I saw and tried, I still needed to see it in action at the Apple Store, with some help from one of the salespeople who could show the little nuances of it. Now I love it.
As for the Ipad Pro 12.9, I've had regular Ipads in the past and always sold them or returned them, because the drawing experience was not that great. The stylii before the Apple Pencil leaved little to be desired. I was Strictly Android, before my Ipad Pro, having Samsung Note phones and tablets. I thought they were the best, but after trying the Apple Pencil at the store, the side by side feature, and other things like speed, I was pretty impressed with what Apple had done with the IPP. So it was worth buying after trying. I could have gone with a Samsung Note Pro Tablet, but it's old tech being 2 years old already and rather put my money towards new Tech like the IPP. I highly doubt I could go back to a smaller tablet size also, after using the IPP 12.9