I have 3 children. I definitely believe in spanking, but only from the ages of 3 to 6/7.
Spanking a child under 2 is abuse, spanking a child over 8 is uncalled for IMO.
But between the ages of 3 and 7, it can be hard or impossible to reason with a child and a few smacks lets them know you mean business. After that spanking becomes unnecessary as you have established your expectations.
At the age of 8 and up if they cross the line a good time out or taking away a privilege usually does the trick, but of course you have to mean it otherwise you start to lose credibility.