That's interesting. I'd be a little concerned that widespread use of that might create more legal issues for Archive.org that wouldn't be problems if it never caught on much. On that basis, I'd probably not use it.
But I'd imagine ideological opposition to such a thing wouldn't be enough to keep it from catching on either.
It depends on your specific case, of course. That 0.4mm is indeed a good rule of thumb. But also, assuming you're dealing with FFF-printed parts, generally if the two parts slide together along the layer lines, it'll feel just a little looser than if they slide together perpendicular to layer lines. That's just due to the ribbed texture inherent to FFF printing. Though printing at smaller layer heights will reduce that effect and also make the parts fit just a little looser over all.
Aside from that, probably the best advice I can give is:
Measure/calibrate for dimensional accuracy. [Here]'s a random article on the topic that looks pretty good to me.
Prototype. Print once, if it doesn't fit right, adjust the model(s) and print again. Filament is pretty cheap, really. Also, depending on your situation, you might benefit from doing quick test prints just to see how well it fits. If the whole print is going to take 8 hours but by spending 30 minutes printing just part of the final product you can prove you've got the dimensions right, it's probably worth it to do the 30 minute print.
Use elasticity to your advantage. Make latches or attachments that snap into place. That's useful whether the parts are meant to go together once and never come apart or connect and disconnect repeatedly. Another use for elasticity is if you need two arms of one piece to friction-grip another rectangulat piece, angle the arms inward just a degree or two. One word of caution, though. It can be really easy to overestimate the flexibility of PLA. I've ended up once or twice with some pretty hard to open latches.
(Full disclosure, it took a little more than right-clicking to download that image. OpenSea apparently purposefully makes it hard to download images. Not terribly hard, though. Only took me a couple of minutes to figure out.)
I don't think the lemmy.ml admins have been coy about it.
If you go to the lemmy.ml home page, at the bottom of the right column is a list of admins.
The first admin's profile banner is a picture of Mao. And the second's profile pic is a photo of Fidel Castro. The other two don't have profile pics that are explicitly authoritarian communist and I haven't had the patience to look through a whole lot of their posts or anything.
Just a couple of Reddit threads (via libreddit.hu) on the topic: one and two. Unfortunately what they link do doesn't appear to be in the wayback machine as far as I've been able to tell.
We might be able to answer the question better if you named the "other platforms" you're referring to. It doesn't seem like an unusual amount compared to, for instance, how much communist/transgender content Reddit had back when Reddit wasn't as evil as it is now. (Who knows what Reddit's like now. I haven't been back since the two-day boycott over the API pricing.)
All that said, some of the communist content here is tankies. (That is, authoritarian communists who spout CCP or other authoritarian communist regimes' propaganda.) Some of the Lemmy instances (like latte.isnot.coffe and lemmy.ml) are run by tankies.
That said, a lot of the communist content here is grass-roots anarcho-communist advocacy by people like me who ideologically lean that way.