Another example is here : «Κενός ἐκείνου φιλοσόφου λόγος, ὑφ’ οὗ μηδέν πάθος ἀνθρώπου θεραπεύεται· ὥσπερ γάρ ἰατρικής οὐδεν ὄφελος μή τάς νόσους τῶν σωμάτων ἐκβαλλούσης, οὔτως οὐδέ φιλοσοφίας, εἰ μή τό τῆς ψυχῆς ἐκβάλλει πάθος».
"A philosopher's words are empty (or vain) if they do not heal the suffering of man. For just as medicine is useless if it does not remove sickness from the body, so philosophy is useless if it does not remove suffering from the soul".
As for the desires Epicurus to be called as empty or vain...Imo Epicurus does not judge the desires for themselves, he does not say anywhere to eliminate our desires for reaching any Nirvana. No, he just judges/measures the consequences of some of the desires. The vain/empty desires usually lead to nothing!
Example : We could say as empty or vain desires those that are based on idealism. e.g. we will save all the world, all we can get along, virtue for the sake of virtue, the greatest good for the greatest number, the absolute justice that exists in the world of ideas, the ideologies/obsessions of all -isms etc etc.