I can't think of a legitimate casual use off the top of my head tho. It may change if hornet provides decent speeds as tor is notoriously slow for most things.
(And, usually, you have to buy such things with cryptocurrency, too, even though they’re perfectly legal both for you to buy and for them to sell; the product’s scheduled status in the US translates to no payment processor [all US-based] being willing to work with the supplier.)
Try buying e.g. Russian-produced pharmaceuticals from Canada without Tor; I’ll wait :)
https://metrics.torproject.org/bandwidth.png?start=2012-08-0... (from https://metrics.torproject.org/bandwidth.html)
To get started with onion routing that's currently in use I'd check out the Tor FAQ [0].
Here's a neat illustration by the Tor project of the protocol: https://2019.www.torproject.org/docs/onion-services.html.en
Here a webpage that describes Tor's v2 design in detail: https://2019.www.torproject.org/docs/onion-services.html.en
Here's the v1 (?): https://svn-archive.torproject.org/svn/projects/design-paper...
You can find some of the onion service addresses from here: https://en.wikipedia.org/wiki/List_of_Tor_onion_services
Facebook on Tor kicked off an interesting discussion: https://blog.torproject.org/facebook-hidden-services-and-htt...
afaik this is because of leakage problems - which can happen silently (eg tor connection goes down, suddenly all your traffic goes through clearnet)
using whonix (https://www.whonix.org/) mitigates this problem
whonix in qubes is also an option https://www.whonix.org/wiki/Qubes
Get on to the hidden wiki, it acts as a reasonable index of common stuff and has links to Tor search engines if you want to get specific. I would also recommend checking out the security section and learning to make sure you're using Tor in a safe and secure manner.
Get a liveboot Tails linux instance running (they provide the operating system on live DVDs you can run from disk, although you can also run it in a virtual machine if you want - but that is considered less safe) and make sure the Tor browser is set to Safest security level (click the little shield next to the address bar), which disables javascript and other things which can leak your identity. It degrades the user experience on some sites, but is much safer in terms of anonymity.
It's all hype tbh, there are very few .onion sites and they are tiny, most are filled with fake woo foo info like "Leaked FBI Proof of UFO's", "How the Illuminati turned my cat gay" that sort of stuff.
As far as legit .onion sites there are maybe 10 of them they all sell drugs and credit cards.
Legitimate use:
It's used to protect you from anyone that might spy on you, hackers, advertisers, social media, governments whoever the bad actor is.
In the current sate of the internet you make too much money being a bad actor to not be a bad actor. I think there is far more legitimate use of tor than illegitimate use. I would say that tor has more legitimate uses than torrents.
If you plan to do something "dark" you should investigate further, but for the curious this is enough.