A similar requirement has been enacted in Canada and what has happened is that Canadians with covid can't return home to Canada and are stuck abroad.
It really gives some teeth to the "do not travel" recommendation - if you get covid abroad you can't come home until you test negative. If you get covid at home and then go abroad you can't come home until you test negative.
I think people who previously would have travelled and just risked it will be a lot more careful now since they can't get home if they are sick with covid. Instead of dozens of flights per day entering canada with covid cases we now have zero [1].
[1] http://www.bccdc.ca/health-info/diseases-conditions/covid-19...