A case in point is his most recent post, RPG Books as Fiction. Go and read it. It's long, but worth it.
Where I think Joseph is precisely on the money (the whole thing is on the money, but on this point it is especially so - if that isn't a tautology) is here:
"I suspect that what [most RPG books] primarily provide, which traditional adventure fiction does not, is a form of meta-fantasy: not a chance to imagine yourself as a fantasy hero, but a chance to imagine yourself as part of a group of RPG players who are, in turn, imagining themselves as fantasy heroes as they experience the material in the book. People read RPG rulebooks, and they imagine how much fun it would be to play a character with a certain set of abilities. They read monster books, and imagine how much fun it would be to encounter those monsters during an RPG session. They read setting books, and imagine how great it would be to participate in a campaign set in that world. They read adventure modules, and imagine how much fun those adventures would be to play in. Then they put them back on the shelf and do something else, instead."
This describes much of my teenage experience of reading RPG books to a 't'. Yes, my friends and I played a lot of games. But how much published material did we actually use for its intended purpose? I can remember a couple of sessions where we played some published Planescape adventures. But the vast bulk of my memories associated with RPG books was paging through them on long car journeys or while on holiday and just, well, imagining what it would be like to use them. "Wouldn't it be great to be in a session where we encountered a morkoth?" I would think as I browsed through the Monstrous Manual. "Wouldn't it be great to have a PC find the Hand of Vecna?" I would think as I read the section of the 2nd edition DMG on 'artifacts'. "Wouldn't it be great to run an all-druid campaign?" I would think as I flicked through the Complete Druid's Handbook. "I'd love to run a campaign set in the Philippines," I would think as I sat reading the Cyberpunk 2020 Pacific Rim Sourcebook. My experience of actual gaming was a pale shadow of the kind of things that my adolescent brain could come up with left to its own devices.
(Not incidentally, I had a similar relationship, thinking back, to Games Workshop books. My friends and I played a heck of a lot of Warhammer, Warhammer 40k, and Necromunda. But being impoverished 13 year olds, we could barely afford any models. We primarily resorted to using a huge mass of ancient lead figures bequeathed to one of us by an older brother or cousin, and we could only dream about the possibilities of actually being able to buy a Basilisk/Lehman Russ Battle Tank/Dark Angel Dreadnought/Orc Shaman Riding a Wyvern or whatever, while paging through 'Codex' books. With Games Workshop, though, the requirement to just sit around reading books and imagining was more or less a nakedly commercial phenomenon rather than anything else.)
It may seem that this makes buying and reading RPG books an extremely decadent and even perverse activity - like a kind of unexciting pornography in which you don't even get to imagine having sex with a beautiful woman but instead just imagine being a horrendous nerd. One view is that it's basically impossible to sink any lower in the hierarchy of cool than fantasizing about playing D&D; you're so tragic that you can't even find a few catpiss-stinking neckbeards to game with and have to simply wish that they existed.
That's one way of looking at it, but when I look back now I can't help but feel that I would have been wasting my time even more egregiously by, for example, playing video games or even reading bog-standard fantasy novels. It might be true that most RPG books aren't particularly well-written, and you couldn't class any of them as being 'literature' in any real sense. But their great virtue is their open-endedness. They don't pretend to be coherent narratives - except for the most railroady of published adventures. At their best, they are a kind of springboard for the imagination: 96 pages of ideas, some better than others, but all of them at least capable of being played around with and squeezed and squashed and stretched and turned upside-down and kicked about until they turn into something wonderful. I may never have got to play in a game in which a morkoth was involved, but I was able to imagine dozens of potential morkoth-scenarios.
In other words, that time spent just browsing RPG books and imagining never-to-be-realised possibilities was a kind of imagination boot-camp, imagination circuit-training, imagination bikram yoga. Since the imagination is a muscle, I think it came in more than handy. Still does, as a matter of fact: I don't think I'll ever run, say, The Veins of the Earth, A Red and Pleasant Land, Qelong etc. at the table, but the thing about the imagination is, there's never a bad time to tone it up a bit.