Why do sites like stackexchange have users sign up for each site?

Question

I am really wondering why the SE community of sites is each under it's own login system --> to me it looks like it passes the session data to each but I am not sure.

The reason why I am asking is that I run a series of internal websites at my company. Right now they are all their own entity and use an SSO service. It is the same user population. I am wondering what are the plus and minuses of having the users go through the sign up process that they have on SE. I can see from a management process it would help me with rights based stuff but not sure each user would want to go through that for a small site.

Note: The question used SE as an example because that is one way I was proposing a solution to my UX. I would like answers on my problem not SE's problem.

Answer 1

Here are two reasons I've been told when I've asked other team members (Full disclosure: I work for Stack Exchange.)

1. Initially when the network was much smaller 3-4 years ago, the team had some issues with cross-domain authorization. You can read more about it here.
2. Another reason someone else hinted at: just because you created an account on UX.SE doesn't mean you'll want one on Math.SE or History.SE or Bicycles.SE. Our communities have very specific focuses and automatically registering everyone for every site will create a lot of empty accounts which helps no one. By making people opt into every community they want to join, we know that every registered user has at least some interest in the community's subject matter. This is important. If you get a lot of "accounts" but no one is ever doing anything, it starts to feel a bit like a ghost town (and IMO a bit disingenuous).

Now I know the team has talked about ways of making the overall experience better. But I don't know of anything in the immediate future.

Answer 2

I think the main reason they do it this way is that if you never use a particular site in their network, it would be strange to show information about you in that site. For instance, you can search users of sites like this and see their information. If having a SE account meant you had an account for each of their sites and someone searched for you on one you've never used and found information about you, then that just wouldn't make sense.

In theory, anyways.

To answer your question, when you're dealing with internal sites for a company, SSO is a fantastic user experience. Unless it's some kind of opt-in program, it doesn't make much sense to have them sign-up for each site. I work at a company with a similar situation. We have sites all over the place for all kinds of things. Some use SSO, some have their own logins. Needless to say, my experience has been much better on the sites with SSO (the sign on experience anyway).

My recommendation: SSO is the way to go.

Answer 3

For an internal website I think you should go with SSO. You are logged in as an employee and should access everything as an employee.

For an external website I dislike SSO. The best example for me is Google. I have a company account to access my agenda and docs. But I also have a personal account for Google+ and another personal account for Youtube. Simply because I want things separated. But I constantly had to sign-out and in when I switched sites. Now I need to use two separate browsers just to be able to listen to music on Youtube while I want to check my agenda.

At StackExchange I have an option. I can either use a "one-click" sign-up to combine the accounts are choose to be somebody else. Perhaps I'm a programmer at work, but at night I like to take erotic pictures and get advice on photography. I definitely want separate accounts..