So far, four people have voted that they do water changes on a timeline...
But nobody has posted any explanation as to why.
This sounds, to me, like people are stressing their fish needlessly.
If not, then we need to hear the actual reason for it.
If someone finds that their nitrates build up, in a shallow gravel tank, with such regularity that they can reliably change the water each week, and they don't care to try some better means of reducing nitrates...that at least makes sense. But, really, it falls into the category of "only change when conditions require", because they took the time and effort to learn the schedule of those conditions, in their specific tank.
People who simply change the water every day/week, because someone told them to...is that doing anything but giving the fish needless stress?