I quite like having functions which take generic "scalars" (double/float/std::complex<double>/boost multiprecision etc) without me having to worry about the specific type everywhere. Of course, sufficiently far down eventually one has to care about the scalar type, but on a high level, it’s nice to ignore it.

The same goes when building abstractions based on this. Tensor<T> instead of Tensor_double, Tensor_float etc.

And then you have all the typical usecases of polymorphism in the wrappers and callers and executables and whatnot which are also to some degree part of "scientific computing".