Why is the optimize argument False by default in np.einsum?

In the docs of the numpy.einsum (which may be found here) it says that for using optimization may increase calculation of contractions with >3 elements. The speed improvement thought, comes in an expanse of memory usage, which will be used during the computation.

So basically it's left for the consideration of the user to decide if he has a sufficient memory footprint to use optimization, and to guarantee that the method will run on most of the devices, which may lack the necessary memory resources.

Cheers.