The context derived from WithContext is scoped to the lifetime of errgroup (after they all return, or any return with an error). This way the function passed to Group.Go can spawn other go routines that will get properly cleaned up.

Why those other go routines would spawn processes that they don't clean up otherwise? They probably shouldn't, but canceling the context should always be safe, and is more likely to safely handle what otherwise would be a bug, than it is to cause a bug.