I have never had more than one camera bag at a time. If you have more than one camera bag, you either have too many cameras and lenses, or a variation of GAS known at BAS.
I certainly have too many cameras. But that's not why I have more than one bag. I have always found use for more than one size of bag, going back 18 years to when I bought my D70 and it was my only camera.
Back then I was ALWAYS on the road for work and always carried my camera in a lowepro bag. That cheap green beast went around the world with me for years. But I had a larger bag for larger kit when I was local and wanted to bring a second lens. This was the case for a very long time until I got a domke to replace the Lowepro -- I hated the domke -- and then got a thinktank.
So I always had at least two, but a few years ago I also got a small holster sized case. Because I could fit it under the cowling of my motorcycle and thus carry a camera when I rode. So I had a think tank PLUS and the smallest possible thing. That's 2 bags, and the bare minimum for my uses, even with one camera.
I still travel for work, but not all the time. Now I visit the office a few times a year, but have to carry a ridiculous laptop with me when I go, so I got a bag large enough to fit the laptop and other sundires. I chose a camera bag so I can still throw a camera in there so I always have one with me. This is easier than when I traveled in the old days with a separate camera bag.
But, if I'm just walking around locally and carrying something small like the Leica with a 50 or the digital, why do I want a bag big enough to fit a giant computer? Just a small bag, big enough to hold a single small camera and maybe some extra film and filters, will do. So that's three bags.
And, if I only had ONE camera, it'd be the Z7 and all of this would all still be true. Tiny bag for the motorcycle, small bag for when I wanted it to wear a larger lens for walkin' around, and a big bag for work or if I wanted to haul it with the big-ass lens attached. Now that I have film cameras, the calculus has not changed.