Cinemagraphs have been described as something between still photographs and video.
Cinemagraphs, or animated stills, can be used to create unusual visual effects. The principle is to take something that, in the real world, you would normally expect to move — and keep it still. The part of the image you want to draw attention to is the only part that moves.
As far as web marketing imagery is concerned, it’s all about engaging the customer.