You shouldn't buy more than your budget can take.
Roger's rent is due, but he really wants to buy a new pair of boots.
Roger wants to make a decision.
Roger puts off purchasing the boots until after his bills are paid.
Roger decides to buy the new boots and worry later.
Roger is able to not end up in additional debt by budgeting correctly.
When Roger writes his rent check it bounces, and he owes the bank additional fees.