I'm steadily working through reviewing all the cards I singled out in my Line Unbroken Against the Shadow Wrap-up post, and that includes least favourites as well as favourites, thus this unfortunate card.

Since this card represents a somewhat iconic moment in the story, it's a shame that the card is so lacklustre, but it really is. This card can of course be used to dodge effects which target questing characters or exhausted characters, but since it's an event, you can't do it consistently and so it only really works if you somehow know that one of those effects is coming up in staging, otherwise you have to keep holding the character back in case of those effects, and you'd probably be better off just having a way of dealing with them when they do crop up and in the meantime benefitting from the extra willpower. (Hobbit Pony of course is a much more reliable option for this since it's repeatable).

The other and more obvious use for this card is to correct for a mistake in how hard you quested by adding another character to make a bit more progress or avoid a threat raise. But then, there are many other ways of doing that - Éowyn, Galadriel+Nenya, Secret Paths, Radagast's Cunning, Fatty Bolger, Westfold Outrider, Hands Upon the Bow, etc - which are more consistently useful. Finally, if there's a particular encounter effect you don't want to hit a certain character or there's a character who you might occasionally need for combat but who can also quest well, Don't Be Hasty! is generally a much better option, because you simply quest with that character and have the extra willpower until you find you do need them ready for combat (or that particular encounter card effect you were scared of turns up), then play the event, whereas to achieve the same effect with Late Adventurer you'd have to play it every round until that moment.

The only cases where I could see Late Adventurer winning out would be perhaps very specifically if 1. You're worried about those occasional effects which do something nasty if the willpower committed to the quest is greater than the threat in the staging area so you want to add afterwards for that reason, but again that's only really going to work if you know the effect is coming. Or 2. You're playing a quest like We Must Away or Conflict at the Carrock where you really want to quest super slowly to start with until your set up, so underquesting is less harmful than overquesting, but you still ideally want to avoid threat raises from questing unsuccessfully. Under those conditions Late Adventurer would win over Don't Be Hasty!, however Hobbit Pony is still better unless you specifically want to pull of this effect with a non-Hobbit.

All in all, this card was a nice idea, but even in the specific cases where it fits it's still really hard to justify using up the deckspace on this instead of something with wider use and more impact.