When giving a child an allowance
Some parents will give a child an allowance as a reward for doing something they should have done anyway. I tend to think children should have certain reasonable responsibilities regardless of an allowance.
I think giving an allowance (once they're old enough) is a good way to teach them the value of money and not something to be used as a carrot or stick.
The allowance money should be used to buy things they want or pay for things they want to do. They need to understand how to manage that money and how to make choices for short or longer term gratification.