I'd just like to add to this. ^^
Some forums have a viewable-to-all forum post with an available series list, stating that the series will be availble to new users after the user's post count reaches X amount of posts. The file-killers (as well as innocent leeches) will rarely go to the trouble of posting so much to get access to the links, instead going digging for direct links to the files elsewhere... hence why having a relatively large post count needed to access them is good, and having the spam section post count disabled.
It's the actual posts containing the links to downloads that would be hidden, or the section that contains nothing but links. To prevent the above mentioned- er
annoyances spamming the hell out of the forums for access, prevent legal issues, and to prevent the files from being linked back to the site if they're found elsewhere.
I can find a file on mediafire right now, having no idea who distributed it in the first place, copypaste the link to it on Google and search, and every single website across the net that has the same URL posted anywhere on it will show up in search results. Insta-DMCA for all if the finder can be bothered. Most often, they'll just send the notice to the file's server, but they have gone after forums simply for linking to them. Hiding the section protects the site from this, if not the actual files, sadly.... (though 'coding' the filenames can help this) And it's not alway liscenced series either. If the original creators cry foul the same thing happens as if it was liscensed in the states, or Aus, or wherever. That's why series get bumped off of YT constantly, liscensed or not. And AMVs.
Also, sites (or people) that never make a single cent from the files still get DMCA notices (I did for an AMV on YT). It makes no difference overall - money just makes them get the slap faster. Premium sections and such.
*cough*AnimeEden*cough* lol
Donations are iffy I think... sometimes sites can go for ages without a problem with the links completely bared for all the world to see, others not... just luck I guess. One site I was on before asked for donations, they only ever recieved one or two DMCA notices dispite having multiple liscensed series, they hid the download links after and they never got another notice again.
/end rant. XD