Peter F Hamilton surmised in his Night's Dawn trilogy that antimatter would be outlawed, but produced by large accelerators parked close to suns in unoccupied solar systems. It was still heinously inefficient, but the high price of black-market AM justified the cost.
Putting speculation aside, we know that AM is fail-dangerous. For all current purposes, we have better alternatives. For long-endurance power sources we have fission. For weapons we have fusion.
I cannot personally think of a common use where the statistical certainty of failure outweighs the risk.
A lot of the yield in H-bombs actually comes from the fission of the depleted uranium tamper - in the Ivy Mike test (the first real multi stage H-bomb) 77% of the yield was generated this way:
The Tsar Bomb test was restricted to 50Mt by missing out the 3rd stage - so it was primarily a fusion device. Had the depleted uranium tamper been in place it would have given the 100Mt the design was capable of - but with horrific fall-out.
My knowledge in this domain is quite limited, but maybe someday somebody will figure something out. Just the thought of antimatter existing is very cool.
Putting speculation aside, we know that AM is fail-dangerous. For all current purposes, we have better alternatives. For long-endurance power sources we have fission. For weapons we have fusion.
I cannot personally think of a common use where the statistical certainty of failure outweighs the risk.