While she's often depicted as malicious, some tales depict her in a more favorable light. Hunters who treated her well, gave her food or willingly let her taste their blood could get more luck in their hunt or be protected from wild animals when they slept.
In some tales she'd have sex with the men she lured off into the woods, and if they satisfied her she would reward them, and kill those who didn't. In some tales she could then give birth to huldrebarn, ugly, malformed children, and she'd then break into homes and replace human infants with her children.
In some traditions there are both female and male huldras, in Norway the male huldra is known as the Huldrekarl, while a similar entity exist in Swedish folklore as Näcken, a naked, beautiful man playing violin by the river, luring women to fall in the water and drown.