Asfaloth is a card most people would find to be obviously very good. The impact it had on the game is large enough that I don't think we'd ever see anything like it nowadays at this more advanced point in the card pool. From a different perspective though, I kind of think Asfaloth is actually under-rated - in that I think people under-rate the value of Asfaloth played on heroes other than Glorfindel.
The use of Asfaloth is easy enough to see - placing progress on a location can equate to directly improving your questing if you put that progress on the active location, or indirectly doing so by putting it on locations in the staging area, which hopefully you can therefore explore without bothering to travel to them. This is especially relevant if the locations in question have annoying Travel costs or effects while they're the active location. Sometimes it may even be the quickest way to get rid of a location which simply has a negative effect while it's in play - if the said location has few enough quest points, you could exhaust Asfaloth after the location was revealed in the Quest phase and then exhaust it again in the Refresh phase, which might be a relevant point if the negative effect triggers at the end of the round. The options for this inevitably expand with the inclusion of additional progress placing effects, but Asfaloth is pretty strong by itself. It was even more significant at the time of its release as there were far fewer alternatives - Snowbourn Scout was a one-shot, The Riddermark's Finest and Ride to Ruin were both one-shots requiring discarding an ally, and Northern Tracker while very powerful, was more limited in timing and more gradual than Asfaloth with Glorfindel, which could be significant if again there's a specific location you want rid of. It's also cheaper than the Tracker and easier to find since it can be fetched by Master of the Forge or Westfold Horse-breeder.
Continuing to contemplate the historical significance of the card, it's quite notable that since the release of Asfaloth, locations with only 1 or 2 quest points have become not quite extinct, but far less common than they were, which I think we have to attribute to the impact of Asfaloth - the designers don't generally want a location to be revealed and then immediately explored for basically no cost without impacting the game at all (since it can be explored between staging and quest resolution). I wouldn't expect to ever see anything quite like it again given that big impact it made. Incidentally, since the result of Asfaloth's appearance is that many more locations have 3 quest points which previously might have been designed with less, you can still try to pull this off if you have some other means of placing a single point of progress.
Asfaloth is great. Honestly, as Glorfindel's lustre has faded a bit with the advent of other heroes who can fill the same role as him, Asfaloth is one of the big things which causes him to still be a top pick because it doesn't work as well for anyone else. The boost to Asfaloth is also one of the best arguments for the otherwise sub-par Glorfindel. That's how good it is. But as mentioned above, I would say Asfaloth can also still be worthwhile on other Silvan/Noldor heroes when it only places 1 progress at a time. I made the point about the comparisons at the time of release, and of course back then there were more locations with lower quest point values, making it easier to get through them relatively quickly without requiring additional location control effects to supplement it. Now if I'm attaching it to someone other than Glorfindel I probably would want to be combining it with other means of placing progress, though that's not an absolute, especially if there are locations with 3 quest points I particularly want to deal with without travelling to them but deckspace is tight for whatever reason. That I think is a coherent argument for Asfaloth being worth it on other heroes at the time of release - 2 resources for 1 additional progress every single round is reasonable to my mind - but what about now? Well, I think it still compares pretty favourably. Other options released more recently include The Evening Star, but that's an event so it lacks the repeatability; Explorer's Almanac takes away from your normal questing progress; Mirkwood Explorer is more expensive and takes time to accumulate the progress before putting it on a location; Warden of Arnor has a similar effect for cheaper, but doesn't give you control over where the progress goes; Arod is the closest, but it still lacks a bit of flexibility since it can only be triggered on killing an enemy while Asfaloth can be used freely in any action window you care to choose.
Now I'm not arguing that Asfaloth is always a good idea without Glorfindel, but sometimes you want that bit of location control, or it might be one of multiple bits of location control. Under some circumstances, the ultimate flexibility of Asfaloth can still make it the top choice for location control even when it's only placing 1 progress at a time. To be honest I kind of prefer it that way, because it becomes a card which is good in some cases but not others, rather than being pretty much an auto-include and thus making for boring deckbuilding.
Overall, Asfaloth is the ultimate in flexibility for location control. If you're playing with either version of Glorfindel and have access to the sphere, you should pretty much always be running it, because it's so good it changed how the designers balanced the game with regards to locations. But don't forget about it when you're playing without Glorfindel either, because there will be times when it turns out to still be really useful.