Uses in Lore
In WildStar's lore, Datacubes are used for the storage of all important data that is performed during a scientific analysis. Presumably, this information is composed of all vital information to the scientific process, such as the experiment and its nature, the procedure of the experiment, all variables and constants of the procedure, hypothesis, test cases, results, and more.
When Datacubes are finalized and all necessary information has been stored, they are placed at a location in the world that is most applicable for the content of the cube. For instance, a Datacube commenting on natural phenomena in the area may be placed near the location where these phenomena occur.
The method in which Datacubes store this data is unknown, but based on the design of the The Elder Cube as well as knowledge on how complex the Eldan are, it is more than safe to assume that the medium is incredibly dense and likely orders of magnitude more spacious than the storage mediums of any other species in the galaxy. As is typical with computer data storage, it is likely possible to store anything on a Datacube. Whether or not they were used for ambiguous data storage, however, is unknown.
Uses in Gameplay
In gameplay, Datacubes are the main source of delivering the World Story to players. They are categorized by the zone that includes them, and always display the individual that wrote the Datacube alongside their Order. Alongside providing a transcript of the entry, vocal recordings of the entries are also included, which vastly enhances the delivery of the information at hand. Additionally, Datacubes can be acquired in any order, but in general, they are placed in a manner where they are discovered in an order that best suits the story. As a result, most Datacubes in an area discuss experiments over a wide range of time in the given area, and any entries sensitive to what the player knows are often locked behind a location with a level too high for the player to be in safely, ensuring that they gather cubes that need to be gathered beforehand first.