So the point of a constitution which sets up checks and balances is what, then, without the checks and balances? And what does another country operating without

So the point of a constitution which sets up checks and balances is what, then, without the checks and balances? And what does another country operating without a ruling document have to do with whether a nation founded under one then re-founded under a second one should follow its ruling document? As a nation state, the US is the Constitution and the government provided for within it.