Is there any documentation for the UUID module?
UUID is an "API" module. It wont do anything out of the box. It is for other modules to use the functionality provided by UUID. 

See the module's README.txt file:


  This module provides an API for adding universally unique identifiers (UUID) to Drupal objects, most notably entities.
  
  FEATURES
  
  
  Automatic UUID generation:    UUIDs will be generated for all core entities. An API is provided for other    modules to enable support for custom entities.    See https://www.drupal.org/node/2387671
  UUID API for entities, properties and fields:    With this unified API you can load entities with entity_uuid_load() so that    all supported properties and fields are made with UUID references. You can    also save entities formatted this way with entity_uuid_save() (depends on Entity API). 
  Export entities to use as default/demo content:    The integration with Features module provides the ability to export UUID enabled entities with intact dependencies and references to other entities.  This functionality depends on Deploy module 7.x-2.0-alpha1 (soon to be    released) and is probably the most robust way for installation profiles and    distributions to provide demo content!
  Services integration:    The integration with Services module alters all UUID enabled entity resources    (nodes, users, taxonomies etc) to be based on UUIDs instead. This way it   becomes easier to share and integrate content between sites. This   functionality is used by Deploy module. 
  More integrations:    UUID module integrates with Views, Token, Rules and provides some CTools  plugins.