Segregation is the central protection in futures, because there is no SIPC equivalent. Customer funds must be held apart from firm assets, reported daily, and may not be used to finance the FCM's business.
Failures such as MF Global in 2011 involved breaches of exactly that principle, which is why segregation reporting is now scrutinised closely by the cftc and nfa.
Example: an FCM holding $800 million of customer segregated funds must show that amount in designated depositories every day. A shortfall of even a few million is a reportable event that can end the firm's registration, regardless of whether it is later covered.
Related: clearing-house, cftc, nfa, variation-margin