Why do we want it to decompose? It's made of carbon, so if it sits underground in a place where it doesn't break down, isn't that effectively sequestered carbon

Why do we want it to decompose? It's made of carbon, so if it sits underground in a place where it doesn't break down, isn't that effectively sequestered carbon? Decomposing it into CO2 and releasing it into the global carbon cycle seems counter-productive. What's the actual benefit of doing that?