Governments (at all levels) and corporations regularly use bonds in order to borrow money. Governments need to fund roads, schools, dams or different infrastructure. The sudden expense of war may additionally demand the need to increase funds.
Similarly, companies will regularly borrow to grow their business, to buy property and equipment, to undertake profitable projects, for research and development or to hire employees. The hassle that giant corporations run into is that they normally need far greater cash than the average bank can provide. Bonds provide a solution by allowing many individual investors to assume the role of the lender. Indeed, public debt markets let thousands of investors each lend a portion of the capital needed. Moreover, markets permit lenders to sell their bonds to different investors or to buy bonds from other individuals—long after the unique issuing company raised capital.