Most government bonds and corporate bonds have a maturity date when the principal must be repaid.
While the few percents of interest every year is generally not a big problem to pay out, when a bond matures the issuer must pay back all the principal at once which can be a huge expense and the issuer can go default if they don't have all the cash at hand by that time.
If the bond issuer issues a bond without maturity, then they only need to deal with the interest payments, which is a fixed amount of money and as the inflation gradually devalues the money it's become gradually less problem to pay it out.
If the price of the bond decreases or after a good year, the bond issuer may repurchase some of his own bonds from the market on his own discretion to further reduce the interest burden.
From the investor side this is kind of security can be bought from the market and sold when they need the cash just like any other security regardless of the lack of maturity. This way this security can be like a stock with a predetermined dividend. Since the issuer only need to pay interest, the credit risk is lower, but interest risk is high.
So far it looks like a perpetual bond is just another kind of security with interesting properties and risks.
But most bonds do have maturity, so what are the caveats? What's the reason that most bonds do have maturity and perpetual ones are uncommon?