What is slot hoarding and does it really lead to cancelled flights?

Qantas once one of the best and most respected airlines in the sky is now in damage control. One of the many accusations being directed at Qantas is that it's hoarding all the best take-off and landing slots at Sydney Airport. It’s brought attention to a critical system in global aviation called slot co-ordination. What are the rules and does it lead to flight cancellations and a lack of competition in aviation?