Perhaps, and in some cases memcpy_s can definitely provide peace of mind, but in a large number of invocations of memcpy (most?), the buffer size is either constant or always equal to the source size (because the buffer was just allocated with that size), and it would feel nannying to me to be
required to write the same size twice.
Empirically, in my experience, a much higher risk is an integer overflow in the allocation in question. Rather than memcpy_s, I'd prefer a malloc_s that takes a count and element size - like calloc, but without zeroing the buffer, so it doesn't feel like a performance waste to use when that isn't required.
