Over-production in layman does not seem to cause a problem, actually will increase the existing stock product. So at any time if needed can be sent directly to the customer
Over-production here could be interpreted to produce the product does not comply with the request eventually makes the excess stock. This excess stock will cause the problems that have to do with quality.
In the context of lean manufacturing, over-production is the waste which must be removed from production systems. The principle of lean manufacturing is to produce products according to customer specifications and demand. If the product exceeds the demand may be indicated occur extravagance.