Maybe trying to avoid struct padding? Although having done a quick test on {arm64, amd64} {gcc, clang}, they all give the same `sizeof` for a struct with 2x`uint32_t`, a struct with a single `uint64_t`, or a bare `uint64_t`.
In any struct where all fields have the same size (and no field type requires higher alignment than its size), it is guaranteed on every (relevant) ABI that there is no padding bytes.
