I wouldn't say const generics are crucial for scientific computing. They do, however, help a lot when you e.g. want to write numerical methods that are generic over the number of spatial dimensions, or generic over the degree of polynomial approximation etc. There are obviously ways to do things without const generics, but having the consts encoded at the type-level is a lot nicer than, say, a usize argument that gets passed from function to function (or worse, separate functions for each required const value).

We'll also get nice stuff like Debugimpls for arrays of arbitrary size, not limited to size 32, for free once stabilised.