The purchaser of a bump-up CD is hoping that interest rates will go up. Once up, the holder can elect to increase the interest rate to the now higher going rate. If interest rates don't rise, there is the opportunity lost of having to keep the lower interest rate for the term of the CD.
When purchasing a bump-up CD, be sure to find out how many times you are allowed to bump-up the interest rate, and whether you have to extend the term of the CD with each bump-up.