Virtual Reality rooms typically consit of 1-6 walls onto which stereoscopic image is projected. The benefits of these are that objects can be viewed in real size, and the immersion is usually great, as in most cases the view area covers whole field of view. And also, as images are stereoscopic there is sense of depth which increases immersion even further. When users are i.e. trained in environment like these, they recall the training sessions better. Of course, as it is usually hands on training, the whole setup is very good in this purpose.
Besides training, many companies are nowadays using these kind of setups also for marketing purposes, as they keep the attention and for sure will be remembered - the experience is very, very good compared to traditional methods.
Another purpose that these walls have been used for is design and research. Large size with lot of extra possibilities (i.e. motion capture) give huge benefits and are keen to refresh creative minds.