What do you mean by "won't thread them correctly"?

The specific use case I had was where the context represented the lifetime of a (shared) TCP connection. I then wanted to use its cancellation to drive the destruction of various dynamic graph elements hanging off that shared connection.

Think a graph of muxes/demuxes in a dynamic message graph while the whole program is a CSP style thing.

I needed something to drive destruction, the context provided what I needed.