The reason we advice bigger solar systems is because of the amount that good quality solar systems have fallen in recent years with the help of government incentives.
In the past when solar systems were expensive, it was probably right for people to find the right size of solar for their house. However, things are not the same anymore. We recommend taking advantage of government incentives to maximise your solar benefits. In addition to this, let your large solar system account for all types of situations such as night time, power outage etc. while receiving money back for any excess energy produced.