There could be tons of reasons to configure a webserver in your home. From a simple blog (personal, just like a diary, or public if you wish to share your thoughts with the web) to host for an home software repository, a web developing ambient and so on.
For an home automation system, a webserver is probably the easiest way to access your house when you are away.
A Raspberry Pi is a quite useful piece of hardware if you need a small webserver. It shouldn't be used for big systems, where hundreds of people needs to connect at the same time and a lot of data is transferred through the network, but for small tasks is perfect!
Now with Raspberry Pi 2, things are getting even better as this new version is much more powerful than the original one.