Distant Stars is one of those cards for which the use isn't immediately obvious so it often gets left out of decks. On giving it some more thought though, one can quickly realise that it enables a wide range of useful shenanigans.
So, break down. Costs no resources which is good, but requires you to exhaust a Ranger or Scout character. This isn't too much of a hardship since there are plenty of Rangers and Scouts but you may want to plan around this when selecting allies for your deck. The biggest non-candidates for this exhaust would be characters who normally quest - on the other hand any character who generally is used for combat or utility purposes (or both) can often give up their action for this instead with no real issues. For example, Ithilien Tracker, Snowbourn Scout, or even a solid hero option in Argalad are all great choices.
Next we turn to the ability. You discard the active location and replace it with one of your choice from the encounter deck. Only works for non-unique locations to avoid potentially breaking the intended mechanics of certain quests, but this is an incredibly powerful location control effect in both parts of it. You can use this to get rid of a horrible location without needing to explore it and/or to fish out a location you particularly want to see. Avoiding negative effects triggered on exploring or placing progress on locations by just discarding them instead is a useful option to have, or equally avoiding negative effects for having that location active/in play; on the other hand any locations with positive effects while active or for exploring them will often be balanced out by a negative Travel cost, which this bypasses. Note also that the replacement location can potentially be one which is immune to player card effects if you wish, since that immunity is part of the game text, which is not active while the location is not in play. So all that sounds pretty good, and that's just considering the card in isolation against a hypothetical generic quest.
The next step is to consider what can happen if we combine it with other player cards. Untroubled by Darkness, Cloak of Lórien and Rossiel can all give you reasons to potentially care about the traits of the active location, over which you have perfect control using this card - though this isn't an option I'd necessarily bother with personally. More recently though, Ghân-buri-Ghân loves this card - since his is equal to the of the active location, this card can let you manipulate his as you like, and unlike the normal run of the game, you don't have to go through the step of having that high location in the staging area counting against you before you get the boost - bonus points if the high threat location also has less quest points than the one you discarded. But the extreme cases came in Race Across Harad, in the form of Explore Secret Ways and the Eryn Galen Settler. With Explore Secret Ways you can negate large amounts of in the staging area (and thus make a nice quest push) if you find yourself looking at multiple copies of the same location, while with the Eryn Galen Settler if you see a location you really don't like you can use Distant Stars, pull a second copy out of the deck, explore it and discard the other with the Settler, thus meaning that you not only removed that location the same Quest phase it was revealed, but you also removed a second copy of it from the encounter deck, ensuring that you're that much less likely to see it again until the deck is reshuffled.
And finally we can consider examples of shenanigans for specific quests. In Journey to Rhosgobel you could pull out Forest Groves and therefore Athelas; In We Must Away you can always find a Troll Camp when you need to remove Sacks; In Into Ithilien you can bypass the Ithilien Road at the start of the game; In Escape from Mount Gram (where this card was released) you can discard an active location to immediately rescue all the cards under it and replace it with a new one with new cards to be rescued; Helm's Deep and Journey to the Crossroads both have locations with positive effects while active which it could be helpful to manipulate, but even better perhaps is using Distant Stars for Siege of Gondor, where you can swap in a Ship location just in time to explore it, thus advancing towards the end of the quest without suffering any of the ill effects for having a Ship location active; and my favourite, the Discover keyword in Ruins of Belegost is triggered when a location becomes active, so Distant Stars can allow you to trigger it multiple times in the same round, meaning potentially multiple Hazards but also multiple bits of Loot (and when you discard the location guarding the Loot you immediately claim it of course).
All in all, Distant Stars may not be a card for every deck and perhaps not for every quest. But if you have a location control focus and/or you're playing a quest which will reward you for pulling shenanigans with the locations then this card can be a veritable goldmine of possibilities for a player willing to give it some thought.