Less crime around the U.S.
If we had an annual purge, I believe the crime rates would decrease dramatically. I'm not saying that it would disappear completely but I definitely think it wouldn't be as high. Considering most people don't want to go to jail. Also it would take out some built up anger that normally causes people to do physical crimes to other people. People would realize "Hey if I wait till the purge I can get away with the crime I want to do."