[Calavar]

Of course it's useful, that's why function modifiers like 'const' or 'virtual' (thinking from a C++ perspective) are widely seen as useful, but making one function virtual doesn't force you to propagate that all the way up the call tree.

[jayd16]

Const is similar, now that you mention it.

[Calavar]

Const is the reverse.

Constness is infectious down the stack (the callee of a const function must be const) while asyncness is infectious up the stack (the caller of an async function must be async). So you can gradually add constness to subsections of a codebase while refactoring, only touching those local parts of the codebase. As opposed to async, where adding a single call to an async function requires you to touch all functions back up to main