Why do some websites have both onion address and non onion address?

Question

Some websites have both public address and also a onion address. By having a public address, the service is no longer a hidden service. What is the point in having a .onion address? As a user, is using .onion address more anonymous than public address over tor network?

Update: From what I understand the following are the reasons,

1. Avoid using tor exit node. This has some benefits.
   1. No one can know how much traffic is reaching the website using tor.
   2. Potentially faster as there are usually small number of exit nodes as they are difficult to run.
2. Once the users bookmark the addresses, they don't have to worry about invalid/compromised certificate authorities and dns servers. The address is self authenticating.

Answer 1

Because they want give privacy aware users a choice.

If a user connects to the onion domain then the whole communication is end-to-end encrypted.

This means that users who wants can connect and use the service without anyone knowing that they are connecting to this website.

If people connect to the clearnet address with a regular browser then the ISP obviously can track that.

And then users can connect to clearnet address through tor - which then goes through a exit node.

The point is not always to keep the website service hidden, it's about giving the users the choice of privacy.

Answer 2

Facebook is one such service offering this. The Tor Blog has an article regarding this topic. It mentions how it is not a contradiction to use Facebook over a Tor Hidden Service. To quote from it.

[...] the key point here is that anonymity isn't just about hiding from your destination.

There's no reason to let your ISP know when or whether you're visiting Facebook. There's no reason for Facebook's upstream ISP, or some agency that surveils the Internet, to learn when and whether you use Facebook. And if you do choose to tell Facebook something about you, there's still no reason to let them automatically discover what city you're in today while you do it.

Also, we should remember that there are some places in the world that can't reach Facebook. Long ago I talked to a Facebook security person who told me a fun story. When he first learned about Tor, he hated and feared it because it "clearly" intended to undermine their business model of learning everything about all their users. Then suddenly Iran blocked Facebook, a good chunk of the Persian Facebook population switched over to reaching Facebook via Tor, and he became a huge Tor fan because otherwise those users would have been cut off. Other countries like China followed a similar pattern after that. This switch in his mind between "Tor as a privacy tool to let users control their own data" to "Tor as a communications tool to give users freedom to choose what sites they visit" is a great example of the diversity of uses for Tor: whatever it is you think Tor is for, I guarantee there's a person out there who uses it for something you haven't considered.