Why own bonds? Let's say you are into derivatives trading and you need to keep a pile of cash lying around as collateral. Bonds are better than cash as long a

Why own bonds? Let's say you are into derivatives trading and you need to keep a pile of cash lying around as collateral. Bonds are better than cash as long as the nominal yields are positive, so you buy bonds (and hopefully not find yourself needing to sell them) which give you almost as much collateral. Or maybe you are into high-yield bonds, which if traded correctly can have better returns than stocks. Not that I am personally interested in playing that game...