I think the largest benefit is for organizations like pension funds which are required to minimize risk. Being able to hedge against specific types of risk (e.g., via a "longevity swap") allows pension funds to allocate their limited "risk budget" in ways which yield higher returns (thereby allowing them to pay out higher pension values).
Derivatives are nice, in that sometimes its possible to separate the risk out from the asset. Consider a $50k loan at 5% with a 1% risk of default.
A pension fund and a hedge fund both have capital, but the pension fund have extremely conservative investors and the hedge fund have extremely risk hungry investors. That loan is not a good investment for either.
So a derivative is created: the hedge fund agrees to make the pension fund good if the loan-taker defaults for a one-time fee of $550 (the cash-value of the 1% risk + a $50 fee). The pension fund now has a $49,450 loan (actually, it will be booked as a $50k load both paying a bit less that 5% interest - the exact amount depends on the running time of the loan) and a $0 risk budget and the hedge fund just made $50 + a 99% chance of $500 more. All are happy, including the loan-taker who might have struggled to get someone to load him money.
(Numbers pulled from thin air for illustrative purposes and lots of details omitted)
I resolved not to play poker again until I understood the game much better.
Ditto for derivatives. If you don't understand the game, you should invest in something else.
As a relatively ignorant layperson, my guess is that derivatives allow productive businesses to hedge against uncontrollable risks.
A business with less risks requires less capital buffer, which encourages & allows for more capital investment and profit-taking.
In a nutshell, derivatives allow businesses to run and grow on less capital, by reducing the amount of capital-on-hand required to buffer against risk.
Is there some other way in which derivatives serve an ostensibly positive function in society? Am I missing something here?