Say I have a default theme for my drupal site. Here I have created views, blocks, etc and styled everything the way I want for the public. Now, as the admin I would like to have an entirely separate theme. No problem, I create a second theme in the themes directory and switch my admin user theme configuration to the second theme. But, what if in my second theme I want to show entirely different content (i.e. Views, blocks, etc). Let's use my front page as an example (front). Right now my front page has a slideshow using Views. This view obviously shows up on the front page no matter what theme I'm using. So for my front page, how could I show an entirely different View (say a list of blog posts) for the second theme than the slideshow View I'm using for the first theme?
The easiest way is to put your views in a block, as blocks are configured per theme. Different themes can have completely different block configurations. A potential issue with this approach is that it does take some more work to get things like arguments to play nicely with views that are hosted in blocks.
Another option which may work for you is to just have the same view themed different ways. Views plays very nicely with the theme layer of Drupal and you can create template files for a particular view or view display. Check out the theme info link in the views admin page to see all the possible overrides for a view. Of course this is assuming that there are some common elements between what you want to show.
A third option might be to display multiple views on the one page, and use the permissions system to ensure only one is shown at any one time. I have used this approach in the past but it did get somewhat unwieldy to manage because as requirements changed I had to replicate the changes across multiple views.