I kept meaning to respond to this and then forgetting to! Anyway, my comment - I'm with you up to a point, but only up to a point. I certainly agree that constraints can help force a writer to come up with plausible & effective settings - "necessity is the mother of invention", as they say. Rules also, though, inherently restrict what is possible - that's the point of them - and so putting in place too many arbitrary rules just ends up constricting things.
To take the schooling example, I'm not sure it is true to say that stability is the be all and end all. An overly regimented schooling system that pushes for stability at the expense of freedom doesn't always help pupils, and in particular doesn't help those who don't otherwise "fit" the system because of some mix of different difficulties or talents. Ill discipline isn't always best handled by stricter enforcement of pre-defined rules; it may require actually talking to children and finding out what the issues are, or indeed allowing children to take some initiative and build things around their own curiosity. Getting the children to mentally invest in a slightly looser structure and rules creates a much stronger structure than trying to make something that's brittle and absolute and doesn't cater for variance.
Likewise, in a project or writing, rules should come as investments from the material and its theming rather than being rigidly constructed on top of it. For example, in my
Tammin stories, I could have tried to produce maps, or rules as to how magic ought to work, in order to force a degree of consistency between the different tales - but adding rules like that, whilst forcing me to think more about the world's structure, would have missed the central point of the stories, which is really to examine a certain moral worldview from Tammin's perspective. As such, the important rule in that case was "is Tammin acting as Tammin ought to act" - and the power of characters around him could vary from zero to infinity as needed around that central point.
I think the final point is the line between creator and audience - there's a distinction between rules that are passed on directly to the audience, and rules that are followed by the creator and could perhaps be worked back implicitly but are never made precisely clear. I think all creators may need to have some sort of organising rule or principle for their work (though it's often quite broad - Tolkien, for example, actually really has Catholic theology as his ultimate underpinning 'rule' for Middle-earth), but there's much more of a trade-off if it comes to making those rules explicit, especially in fantasy. Fantasy relies in part on the 'rules' of day to day existence as we know it, and on breaking those rules in unexpected ways. Being able to break those implied rules of physics and life at will and at random (at least random as far as the reader knows) can be a genuine strength, because it speaks to a human desire for discovery and wonder at the unknown. A universe with
totally rigid and explicit rules perhaps risks losing that key element of fantasy - a sort of inherent hopefulness and wonder at the possibilities?