I've seen a few posts ranting about Discord getting used as a host for files/projects/mods. I agree with those posts - it's unnecessary, and Discord is liable to just nuke your server if they find a reason to, and those files are lost forever. But there's a whole bunch of other reasons why you shouldn't be doing that. Let's go over that.
1. It's a hell of a barrier to entry for people who don't want to join servers.
This can be for a lot of reasons. I, for one, don't enjoy the experience of joining a new server. One never knows how many click-throughs you need to do to gain access to the channel you need, how many Roles you need to React for, what kind of user-approval system they have in place (or even if they don't have a "system"). But the worst one, IMO, is when a server has new user join announcements enabled, and a community that likes to click on that "wave!" button. I'm here for a file, damn it, not to join yet another social circle. I'm socially awkward to begin with and I'm not looking to Make New Friends, especially not if said "friends" are... let me start another heading here, first.
2. If your community sucks...
Nothing gives you a better sense that I shouldn't be here than if the community surrounding your all-important download links is a bunch of assholes. This can take many forms. It is worrisome if the server has a "memes" channel, and moreso if the quality of those memes is extra low. If I spot even one Pepe or deep-fried extra-loud video, I'm out. Other red flags IMO include if any given channel is moving faster than I can read (and I can read pretty fast, mind you), if you have a "venting" channel at all (even if I have to opt in to it), if there's a news/politics channel that I don't have to opt into, 18+/NSFW channels visible by default with no verification (even if they're flagged), casual slurs thrown around by anybody... if I'm seeing any of that, I'd rather leave your server than keep looking for your download.
3. It is not searchable. Period.
Discord has been steadily making their search bar less and less useful. If I need to scroll back in a channel at all to find what you want me to find, you have failed. If your project's server has a bunch of channels that aren't where the download is at, you have failed. I should not need to use that search bar at all, let alone struggle with however the Powers That Be have ruined it this month. This goes in addition to the fact that you can't search a Discord externally from Discord, either; if I search Google/DuckDuckGo/et al. for your file, I'm far more likely to find some old, possibly outdated version being distributed by somebody else who was frustrated by it being on a Discord. This'll lead to... let's start another heading here.
4. If you don't support it, someone else will, without your approval, and they'll do it wrong too.
Suppose you made some big release and made it exclusive to your Discord community. It spreads around beyond the people who hang out with you. But oops, there's a bug in it, better push that hotfix right quick! OK, cool, now every copy of that release on your discord has been patched and the bug is gone. Except months, even years later, you keep getting new people joining who report that same bug. The bug you fixed ages ago. Turns out they're not getting their copy from you, they're getting it from some third party who posted it to ModDB (who patently Do Not Care when a project is uploaded by someone other than its creator). If you and your project do not have a presence outside of your Discord, someone else will provide that presence, and I guarantee you, it will not be the kind of presence you want.
5. You are not being as secretive as you think you are.
Remember, if your reason for not hosting your downloads on a Github, Google Drive, or Dropbox is that "they'd take them down for copyright reasons", remember that Discord is not your friend either. I've heard of entire servers getting nuked because a few people hit Report on them, all those files gone. Discord owns everything that goes through their servers, and they will absolutely not take your side when greater interests are asking them to remove something.
6. Bug-tracking and scroll back.
If your project's presence is 100% Discord, you had better have a good way to track issues and to-dos. Because if someone's reporting a bug with your thing, and you don't act on it immediately, other chat (or even other bug reports) will scroll the original report off the screen where you will likely never see it again. I don't care how good your memory is, things can and will get lost in the wash this way. I recommend having your project on Github or Itch, where commenters are guaranteed to already have accounts and can receive notifications if there are replies to their issues.
I've seen this line of thinking from the other end, too; users join a discord expecting to be able to report bugs on it, not realizing that their reports will get lost in the wash. Nip that in the bud immediately. Anybody that wants to report a bug should do it through the web issue tracker, whichever one you use. Even a phpBB forum is better than letting it scroll back in the chat.
Anything further?
I think I've made enough points here, but I honestly do want to hear if anybody can tell me the advantages to this. What's the motivation? Why is this so common? Surely there must be some merit to it if enough people do it, right?
Adding:
Discord gained a lot of visibility for being as free as IRC for chatters, without the need to host your own server, with friendly bells and whistles in the UI that made it approachable at a time when Skype, Teamspeak et al were floundering a bit for various reasons, in the wake of venerable AOL falling to the reaper, and so forth. As a casual easy option it found a quick niche and grew to fill.
In its original role, it’s still largely fine: a central small-community organizing hub for groups organized around a core interest (which is sometimes just “friendship”) to connect for text and voice chat; a groupchat not tied to phone messaging logs and available on multiple platforms. It’s fine, it’s “free”, you don’t need to set up your own server for chat hosting, you get kicky screen names and avatars and shit.
That “it’s free!” is what attracted a lot of RPG devs in my personal experience. Live chat with both co-writers and fans! Live feedback! Instead of looking for group forums that would require you to get a new couple of apps just to play, you can meet people in live chat and then hop right there into a voice chat, it’s convenient, it’s free, and you may need mods (if you’re bigger than a small friend group YOU NEED MODS) but you don’t need tech people and server maintenance admins and all. Easy file sharing! All in app!
I imagine that a lot of coding and videogame dev communities formed the same way, for the same reason, and this isn’t going into the Official AAA Game discords which have their OWN reasons to keep things controlled (see “if you don’t, someone else will” above, for starters)
But as anything more than the intended purpose, discord is rather ill-suited, for all the reasons listed above and then some.