I have used the boat/water taxi service on quite a number of occasions since they launched their Venice service and in my case because I always book hotels that are on a canal and have a private jetty/drop off point I have never had to finish my journey on foot. Because there are only two ways of getting around the main two areas - boat and walking - there is no choice but to walk from the nearest drop off point if you are staying somewhere that does not have canalside facilities they can only take you by boat and you have to walk the final bit. Don't worry though as nothing is far from a canal. Enjoy the trip though - it is a very unique experience!