likewise any other kind of adventure, it doesn't necessarily mean the protagonist would make an impact to plot/final resolution (thus is appreciated when done correctly).
It can be a purely explorative game where it's up to the cunning of the player to get to know more about the lore around him/her. In a classic adventure game you would be given the option to destroy an item for whatever propose... Optionally this item can carry additional info on the story (ie: a book, an audio tape, a keycard for a special room etc) and its up the cunning of the player to access this data (hasteful play through ones will let you lose lot of details)