É completamente inútil
De acordo com a Memória Alfa :
Though once considered very valuable, by the 23rd century the Federation considered [gold] almost worthless, except for decorative and functional purposes. (TOS: "Catspaw"; TNG: "The Last Outpost", "Time's Arrow"; VOY: "Muse")
No entanto, essa é a Federação; os Ferengi ainda consideraram valioso até bem tarde no século 24:
Dialogue in TNG: "The Last Outpost" and "The Perfect Mate" suggested that, at least as late as 2368, Ferengi considered gold valuable. In "Little Green Men", Quark says to a 20th-century Human that "gold is good" while discussing what humans could trade for advanced Ferengi technology. However, by the time of "Who Mourns for Morn?", Quark described gold as "worthless", seemingly contradicting the earlier assessment that gold had "good" trade value.
A razão para isso, como explicado na resposta de Philipp acima, é provavelmente o replicador
One explanation for this apparent devaluation of gold was the fact that the Ferengi had only recently made First Contact with the Federation. Replicator technology, if introduced to a gold-based economy, could send markets plunging. This may have happened to the Ferengi, who would have experienced a massive gold market crash as a result. Then again, gold may have lost value for some other reason. The comment in "Little Green Men" may be in the context of a pre-replicator economy, especially since he stated his intention not to go back to his own time, remaining in the past and ruling the Earth within a year.