GUIDs are not really designed to be used as security tokens -- they are unique but not secret. The (pseudo)-random process that generates them is not necessarily cryptographically secure.

There are a variety of reasons why developers use globally unique identifiers (GUIDs), such as assigning unique identifiers to classes or when dealing with databases. This tip contains sample code ...

Non-random GUIDs UUIDs or GUIDs, whichever you prefer to call them, are a Universally Unique IDentifier, and they get used all over the place.