If you look on Right-Click Select (the feature request site for Blender), you'll notice that one of the frequently-requested features is the ability to save or otherwise export just part of your active .blend file to a separate file. In fact, as of this writing, there are 7 different requests for this feature with a combined total of 176 up-votes. Considering the fact that the current top request has around 500 up-votes, this is clearly a feature that a lot of people are interested in.
And they should be interested! This is a feature that's very helpful for managing data and assets in larger projects. Let's say you're working on a scene and you've added a prop to it... but then you realize that prop is going to be necessary in a bunch of different scenes. It'd be really nice to push the prop to its own .blend file so you can link it from your other scenes. That kind of thing can happen all the time in larger projects.
So to support the artists and studios that would have their lives made easier with this ability, Orange Turbine has created the Export to .blend add-on.