Perhaps the most important and lasting legacy of Instant on the history of search is the fact that it introduces a new concept called CSI for Conversational Search Interaction as mentioned by Ben Gomes, Distinguished engineer at Google in one blog post.
The CSI that Gomes is refering to is the fact that Google Instant automatically refreshes the search engine results page without being prompted by the user.
Google manages to do that trick by converting the SERP (Search Engine Result Page) static HTML page structure into what is essentially an Ajax application, a move that will have profound consequences on the way the web moves.
What's interesting as well is that the URL sneakily changes every time and is being recorded as a separate SERP altogether. This means that overnight, the number of searches carried out by Google users exploded (although Google already said that it doesn't count all actions as page impressions).
What does that leave us with? Google managed to cram more search results per unit time, making search results even more relevant for the user which in turn should raise the click through rates (CTR) and bring in more revenue for Google.