It has historically been used to allow for bonds to have uniform repayments across maturities (when the principal of a bond becomes due) - useful in the context of a bank wanting to hedge risks such as interest rate risk, repayment risk (if the bond is callable it can be paid back early, which means the bondholders have cash yielding ~0% instead of whatever the bond yield was)
Mortgages, though not traditional bonds (in that it's not a sophisticated company borrowing) are, depending on the jurisdiction, treated as bonds because they get packaged up and sold as bonds - the underlying bit of financial engineering that, after serious perversion, gave us the 2008 credit crisis
It has historically been used to allow for bonds to have uniform repayments across maturities (when the principal of a bond becomes due) - useful in the context of a bank wanting to hedge risks such as interest rate risk, repayment risk (if the bond is callable it can be paid back early, which means the bondholders have cash yielding ~0% instead of whatever the bond yield was)
Mortgages, though not traditional bonds (in that it's not a sophisticated company borrowing) are, depending on the jurisdiction, treated as bonds because they get packaged up and sold as bonds - the underlying bit of financial engineering that, after serious perversion, gave us the 2008 credit crisis