Neutrons are required for the stability of nuclei, with the exception of the single-proton hydrogen nucleus. Neutrons are produced copiously in nuclear fission and fusion. They are a primary contributor to the nucleosynthesis of chemical elements within stars through fission, fusion, and neutron capture processes.
The main difference between beneficial and harmful friction is that beneficial friction is necessary for performing different activities while on the other hand, harmful effect of friction is destroy different parts of products and machines. examples of beneficial friction are walking, holding things, rubbing hands to produce heat, running etc whereas examples of harmful friction are destruction of sole, slipping, tearing of machine's part, Wet roads and Mudslides etc.