Wifi Shield Examples - Why join other wifi networks ?

I have seen some examples of Wifi Shield, an interesting observation I found is that, in every example, the programmer is trying to connect to another wifi network, so that there may be an internet connection for the device(wifi shield) I suppose. Does joining the other network’s give device access to internet ?

I am looking for examples that do not connect to any other wifi networks, because the device itself is emitting a wifi network…may be I want to make files on SD card visible to clients within the device’s wifi network.

Thanks,
Pradeep

Well, typically you need to join another existing network because it is somehow connected to the internet and many projects are trying to either get data out to somewhere else or get some data from somewhere else (time, weather etc.). If you don't need internet access, then you don't have to join an existing network and can indeed exist as your own little "world". You can configure the arduino/shield as a small server for example.