Steam oven proponents claim that steam cooking not only reduces cooking time, but also lowers the fat content of food. Where dry heat cooking tends to rely on added fat to keep meats from drying out, meat needs no supplementary fat with steam cooking, and will definitely not be dry because of the constant injections of steam.
Steam cooking also retains more vitamins and flavour than other cooking methods and so can be considered a healthier way of preparing foods. Speed is also a plus in steam cooking. Consider cooking a whole chicken. In a standard convection oven that chicken would take about 90 minutes to cook. In a steam oven, that same chicken would be on your plate over an hour sooner.
There is a downside to steam ovens. They don’t brown. This can be easily overcome by browning meat before it goes into the steam oven, but of course this doesn’t work too well for baked goods.
The majority of steam ovens I see are of the built-in variety. In many cases they are designed to coordinate (finish and size) with other appliances (microwaves and wall ovens most typically) for an integrated look. The kitchen I'm showing here features a Miele steam oven paired with a standard wall oven.
A new appliance for a traditional cooking technique, the steam oven is worth a look for the serious cook.