It does collect data for use within the OS itself, to assist the user with searching their own system. My understanding is that none of this is ever sent out over the network. You can turn off individual data sources, or disable data collection altogether and use traditional command line tools for searching for your stuff. The linked screenshot is of the default settings under the Privacy tab in Settings, with a tooltip explaining why you would want to turn off collection.

http://i.imgur.com/1FbMQkm.png