Advantage of saving `.npz` files instead of `.npy`

What is the advantage of saving `.npz` files instead of `.npy` in python, regarding speed, memory and look-up?

the .npy format is:

the standard binary file format in NumPy for persisting a single arbitrary NumPy array on disk. ... The format is designed to be as simple as possible while achieving its limited goals. (sources)

And .npz is only a

simple way to combine multiple arrays into a single file, one can use ZipFile to contain multiple “.npy” files. We recommend using the file extension “.npz” for these archives. (sources)

 

• If only use np.save, there is no more compression on top of the .npy format, only just a single archive file for the convenience of managing multiple related files.
• If use np.savez_compressed, then of course less memory on disk because of more CPU time to do the compression job (i.e. a bit slower).