Depends on the type of training. Walmart is using VR to simulate Black Friday scenarios in which a fully-immersive environment would be more useful than an overlay.
Several AR companies are working on just-in-time knowledge to allow people to do tasks without prior knowledge. We've invested in that area and I wrote on the topic here:
Several AR companies are working on just-in-time knowledge to allow people to do tasks without prior knowledge. We've invested in that area and I wrote on the topic here:
http://www.businessinsider.com/augmented-reality-could-slow-...