This from a blog I follow - http://www.ikigaiway.com/2009/thoughts-on-footwear/
The concept has been around since I started training (late 70's) at least. Some even call it environmental training. Adding in street clothes, uneven surfaces, dim lighting, etc. And I trained in a very 'traditional' way - remember the first Se Ping Ma lesson? Usefulness was always demanded. Still wondering about some of the crane beak strikes...
Also, some believe that training barefoot on concrete sucks the 'chi' (life force) out of you and is unhealthy. Training on grass, ground, wood, even mats is preferred.
Just my two cents worth.