To be fair, stating the obvious, which she does quite a lot, is also quite advantageous. Like, sure, that Klingon Captain seems angry and insulted, but what if he's just a really good actor trying to deceive a Federation ship? When Troi goes "Yup, he's angry and insulted" that would basically be the go ahead to assume he's telling the truth and act accordingly.

But TNG writers usually only seemed to remember there was an empath on the bridge at the last second, so they just wrote in she can't sense anything