The so called "poll that matters" that supposedly makes the other polls irrelevant, only matters for one thing (two if being nitpicky) 1) picking the 4 playoff teams 2) deciding NY6 bowls.
BUT (and yes it's a big but) that poll is never released again after the playoff is determined, so if one cares about final rankings n such (outside the team that wins the playoff), the other polls are the only ones that are relevant.
Now having said that, I do wish they would make up their mind which standard they want to use to make Kelly's performance look better, ranking at time we played them -or- current/ final ranking. I personally think the current/ final ranking metric is more accurate in determining the quality of teams you've played, but it's annoying seeing them switch back and forth from one to another based on which makes Kelly look better at that moment.