I know that audio guides are a good way to control visitor flow and visit times, ensuring people get an overview while also pushing them through sites at a suitable speed. They can provide a reliable service not always possible unless you employ a large pool of highly trained staff, such as language options, BSL on video screens, child friendly tours. They can be a flexible tool, such as at Apsley House, offering visitors a choice of tours depending on their specific interests. They allow historical venues to be free from obtrusive signs. From the visitor's point of view, their experience can also be enhanced by a good audio guide, with music, interviews from behind the scenes staff, and video clips.
However, using so many audio guides in a short time highlighted two - to me - unpleasant side effects. The first is how much people were attuned only to the audio guide, to the detriment of all else. The second was the isolation of the user.