That rune decreases lust increase from any source by 50% (rounded down). It's made to completely shut down passive lust gain as long as there are no other modifiers. Though I suppose that that might be confusing
The using items while asleep thing is mostly there to make things more fair. Sleep is already incredibly powerful and dangerous and usually you'd have partners to help you out. While it doesn't make much sense, the game would get a pretty big difficult spike without it, I think