Various techniques are factors in edge longevity for sure. But some guys have really sensitive skin, and can sense edge deterioration as soon as it happens. For them frequent touchups may be in order to make sure their blades are in tip-top shape. This is why I don't really like giving a figure for how long a blade should last. If a newb hears that a blade should last months before a simple touchup they may think they are doing something seriously wrong, which perhaps they are or they aren't, who knows? Therefore the correct answer is "whenever the razor needs a touchup, do it".