In a dedicated Trap deck this cards it's a must have, especially at low player counts. It can be useful also in a big Fellowship, even though looking at (usually) 2 to 4 cards is sometimes only enough to plan for a single quest or combat phase. Still being able to use it whenever you want (and to get rid of one of those cards) can be quite good, especially in quest with obnoxius tests like Hunt for Gollum, A Shadow of the Past or Mount Doom.
Action: Choose an enemy with an attached Trap card. Look at the top X cards of the encounter deck, where X is that enemy's printed . You may discard 1 of those cards. Return the rest to the top of the deck, in the same order.
The Drowned Ruins #90. Lore.