I also find it difficult to conceive of a case where adding noexcept would lead to slower/longer code, other than arbitrary noexcept overloads such as TFA.
The article describes the performance implications of the hash tables storing hashes. That it decides to do so based on examining noexcept() of passed in types doesn't make noexcept a pessimization itself
And, as you can see on the sibling thread where I'm being downvoted, there is an actual pessimization: since a noexcept function requires an eh_frame, it will not be able to tail-call (except for noexcept functions).
I also find it difficult to conceive of a case where adding noexcept would lead to slower/longer code, other than arbitrary noexcept overloads such as TFA.