From what I've read, doing that was a pretty expensive process. Also from what I've read, she was aware she was breaking the rules.
Why did she do that?
If you wouldn't mind, how about pasting the pertinent facts I'm IGNORING?
In the link provided, it says she set the server up while she was a Senator, before she was Secretary of State (in fact, it seems like I've heard it was set up shortly after Bill left office). My understanding is there is no rule/law prohibiting Congress people from having private e-mail or private e-mail server. In fact, I believe Congress is, by law, shielded from FOIA requests and are not bound to retain any digital records. Thus, Clinton was NOT breaking the rules when she set up her own e-mail server (which is part of the link you were sent). Furthermore, from what I've read elsewhere, it's not an uncommon practice. Actually, allow me to rephrase. It's not an unprecedented practice, either private e-mail or server.
As for "why"? There are many many reasons one would like to have a private e-mail server and control what happens on the server.
Of course she was aware that she was breaking the rules, she created her own private e-mail server for the express purpose of breaking the rules, to hide her crooked dare I say treasonous, correspondence.
Under the timeline with which I'm familiar, this is untrue.
I think it's also important to separate the reasons for creating a server and the reasons for exclusively using a server. The reasons for creating a private e-mail server are not at all relevant. They really aren't. I could create an e-mail server, if I felt like it. It's not hard.
The reason to exclusively USE a private e-mail server, especially in a position Clinton held, is a much different topic. And, like many in this thread, I don't buy for a second it's because she didn't want to carry two Blackberry phones, but rather used it as a workaround to avoid FOIA. Whether it is illegal or not seems to be something of a gray matter, but if I remember correctly, it did violate Department policy. But, since she's no longer in the State Department, I don't exactly know what one does about it.