Adding videos to a website is something that is on the increase with many of the most successful companies doing it and even the smaller local companies following suit. For many websites, having a video on there is a great selling point and allows you to personally interact with the customer almost face to face. This gives some visitors a little peace of mind and often may just be enough to sway them in to contact you or making a purchase.
Auto playing videos on the other hand can have the exact opposite effect. If you land on a website and a video starts to automatically play you may be a little confused as to where the sound is coming from or even how to stop it. Some sites are also programmed so that when the page is refreshed or another page visited, the video will start to play again. I recently saw one website that had two different videos playing simultaneously which was extremely confusing and very annoying.
If you do decide to have a video on your website, think very long and hard before asking the programmer to set it to auto play.