These types of loans offer a low interest rate usually for the 1st year of the loan.
The rate may be fixed, variable or capped, meaning that if interest rates rise your rate will not go up, but if rates fall that rate will go down and you will benefit. Once the Introductory or Honeymoon period is finished the interest rate usually reverts to the standard variable rate. The advantage of an Introductory Rate is that it offers borrowers a chance to reduce the principal quickly by making extra repayments.
The main disadvantage is that most banks charge a slightly higher rate after the introductory period. To quote Sir Henry Royce "The quality is remembered long after the price is forgotten."