I’ve been using a seat pad for a few years. I got my first one in 2017: Impressed by my friend’s use during roadside snack breaks on tours, I figured I should get one for my first ever backpacking trip. Unlike bike touring, there wasn’t going to be a picnic table at my campsite. It’s been an invaluable tool for bike camping and touring, and the inflatable ones pack pretty small. But like any inflatable pad, they take time to deflate and pack. Plus, there’s the tendency to overinflate no matter what. Finessing the pad to the right pressure takes a little time.
Enter the simple folding butt pad. I saw that Grant Petersen of Ye Olde Rivendell sang the praises of the Therm-A-Rest Z Seat Pad. I didn’t think too much of it, since it’s bulkier than the inflatable seat pads. Then I found one for free, most likely from the Lost And Found from the hostel. (There’s not a lot of things I miss about that job, but the shortlist of things I do miss include the Lost And Found and staying at other hostels for free.) So I started using it. It may not be as comfy as the inflatable one, but it’s a lot easier to use: unfold, sit, fold.
Because of the ease of use, I’ve been carrying it around a lot this year. I can easily strap it to a Carradice, put in a basket, or bungee to the rear rack. The Year Of Coronavirus means a lot of sitting outside, mostly on picnic tables. So having an extra layer of comfort and insulation between a slab of wood or concrete is really handy. And if it’s wet out? My butt don’t get wet from sitting down! That also goes for any “questionable” seating area. And this style butt pad is very easy to clean. And since this pad isn’t inflatable, I don’t have to be as cautious about things that could poke it.
So now I carry around this butt pad more often than I don’t. If you spot me with it attached to my bike, I’m most likely not going to camp, just tootling around.
Urban Adventure League 
100% agree on seat pads! I still have my two old seat pads from my AK hiking and climbing days. They’re just cut-off sections from the closed-cell foam sleeping mats that I used…and abandoned when I graduated to a Therm-a-Rest. The Therma-a-Rest was a godsend when sleeping on snow. I now use my old seat pads (we called them sit pads in the 80s) as kneeling pads when doing house and yard work 🙂
I’ve been considering something like this. We too are spending more time on patio and picnic tables and having to wipe them down from rain or dew and now having to deal with the cold, especially the metal chairs. I thought I may have found a solution in a ditch the other day. It looked like it might have been one of those gardener kneeling pads but turned out to be a cutting board.