The detailed study of the low energy Secondary Electron Yield (LE-SEY) of technical Cu for very low electron landing energies (from 0 to 30 eV) is very important for electron cloud build up in high intensity accelerators and in many other fields of research. However, LE-SEY has been rarely addressed due to the intrinsic experimental complexity to control very low energy electrons. Furthermore, several results published in the past have been recently questioned for allegedly suering from experimental systematics. Here, we critically review the experimental method used to study LE - SEY and define more precise energy regions, in which the experimental data can be considered valid. E-cloud simulations are than performed to address the impact of such results on electron cloud predictions in the LHC.