From the esri help:
"Global ID and GUID data types store registry style strings consisting of 36 characters enclosed in curly brackets. These strings uniquely identify a feature or table row within a geodatabase and across geodatabases. This is how features are tracked in one-way and two-way geodatabase replication. Developers can use them in relationships or in any application requiring globally unique identifiers. In a relationship, if a Global ID field is the origin key, a GUID field must be the destination key. You can add global IDs to a dataset in a geodatabase by right-clicking it in the Catalog tree and clicking Add Global IDs. The geodatabase will then maintain these values automatically. You can create the GUID field as well, but you must maintain its values."
AmigoCloud takes advantage of the GlobalId being managed by the geodatabase to provide 2 way syncing between AmigoCloud and the geodatabase.