I think it depends on what you mean by adjustments? Changing your play calls? Blocking schemes? Personnel? Some are easier done on the fly. As we know, the 11 man game of football can be treacherous to a team not on the same page. If you are changing something complex such as a blocking scheme, it is probably best to wait until the half to make sure everyone is on the same page. That being said, minor adjustments are being made all game and not just at half. It is my thought that major schematic adjustments wait until the half, as to not abandon the game plan too early.
It works for BB and TB12. They are the best second half team in football