For example, a firm may have issued bonds during a time when interest rates were high. If interest rates have come down significantly, the firm may want to conduct a new bond offering at a lower rate and then use the proceeds to conduct a debt tender offering in order to buy back the more expensive bonds as a way of cutting costs.
Furthermore, a highly leveraged firm may also wish to use its retained earnings to buy back bonds in order lower its debt-to-equity ratio. Doing so will give the company a greater margin of safety against bankruptcy because the company will be paying less interest.