We only fly the 172 and 177, but there are a few companies that use twins. I believe the twins are at the request of the pipeline companies or when they cover areas that are past single engine glide range off shore. One of the pipeline companies that I fly for wanted me to do a weekly check on a buoy that was about 25 miles out in the gulf, this was just a short term thing but the company I work for was going to request that we use a twin, if it was going to be an extended item.