Functionally it would mean cheap, green, unlimited energy for mankind. Hydrogen is just everywhere and there are no harmful byproducts, unlike fossil fuels or nuclear that are non renewable resources. Granted they use mostly dueterium and tritium currently which are a little more rare and expensive.

Important to note that the reaction didn't really get "more energy out than they put in" in fact they put in about 100 times more energy than they got out. However it is still a massive achievement, but I wouldn't hold my breath and wait for fusion reactors to come online. Probably about ten more years.