When your four year old boy or girl misbehaves, when they know that what they have done is wrong, and goes against what you have told them to do, a smack or two on the hand or bottom is a legitimate form of discipline.
For some children, the naughty mat or time out work well, and their parents may find that they do not ever find the need to smack their child. However, there are plenty of children who do not learn their lesson from being seperated from the family for a short period of time.
Many children will not understand why they are being put in time out. For many children, time-out will be more harmful - make them more upset than one or two smacks would.
With a smack, the discipline is over promptly.
Smacking must never be used while the parent is angry, or while the child is moving about - ie. running around the kitchen table. The child must understand what rule he/she has broken, and must agree to being smacked. The parent must make sure that the child does understand how they have misbehaved, and why they deserve to be smacked.
Any other form of hitting for the purpose of so called "discipline", is unacceptable - and abuse.
Watch the below video, where the "Timaru Lady" from the "riding crop case" explains to you what really happened - and backs up what I have written above.