I think it depends on the experience of the cook. When I was young I measured everything and followed recipes exactly. That is how I learned the classics.
That was a long time ago, now I measure by dead eye reckoning and make my own variations on the classics as well as making up my own recipes from scratch.
As with any art I think you have to learn the rules first and then throw them out to advance yourself as a cook as well as the art of cooking itself.