Why would I want to use Universally Unique IDentifier (UUID) in Drupal?
If you want to create an UUID for you content you should use the modules. UUIDs can be used for content staging and such.

The problem is that Drupal uses serial ids for the content (nodes), so if we have the same site installed different places, the id for the same content most likely will be different. (fx in one environment the node id might be 137, while it on another might be 153)
This makes it very hard to track changes on the same content in different environments. The idea with UUIDs is to create a id that is the same on all environments.

So you could have content writers work on a stage site, have it reviewed, and the put the changes out on the production server, without messing everything up in the process.