Speed is essential, but some curricula value it too much. The core of every mathematics classroom should be problem solving. Ponderous problem solvers need to be protected.
I am not making the case against memorizing basic facts. Students absolutely need to memorize and be able to quickly regurgitate 7 x 9 = 63. However, this is not a pre-requisite for getting into tough problem solving. Math “facts” like 4 + 5 = 9 are not pre-requisites to thinking. Kindergarten students and younger should be exposed to tough problems that take time.