It requires one less mouseclick. If you want to pretend you're using the old Google, you can just close your eyes while you type, randomly click your mouse, then open your eyes. You will have before you the same results that original Google would have returned.
Unless you get confused by the "Instant" feedback along the way (like you somehow get distracted by shiny other searches that Google recommends, forget what you were originally searching for and get "tricked" into some new query), it shouldn't be an issue.