I am not fond of ‘soft’ magic. All the magical events in my primary fantasy mythos follow strict, generally well defined, ‘scientific’ rules. They may be ‘rubber science,’ as the science fiction community terms such plausible but invented rules, but they remain constant. In that sense, my fantasy could be alternatively labeled science fiction.
Most fantasy has used soft magic over the years. And centuries and millennia! Stuff just happens without much explanation. Gods and demons have powers. Sorcerers cast spells. Names have power. And so on. You’ll find it in Tolkien. You’ll find it in Le Guin’s ‘Earth-Sea.’ That approach also spills over into science fiction when telepathy or the transferal of consciousness occurs, often without explanation. I assiduously avoid such things. Even at best, they become a crutch.
As can be soft magic. It’s far too easy to fudge what magic can do when there are no strict rules. Ultimately, having those rules requires us to think creatively about how to work with them. Rather like writing poetry in form; finding the words that work properly can lead us to new insights on meaning, point us in new directions. We will find no new roads if we don’t run into a few obstacles.
I might add that the rules of magic in my stories are also rooted in science (yes, of a sort). They are not just arbitrary rules that have no explanation — or ones that are, in themselves, soft magic. Sanderson’s work tends that direction. However, it is recognized in the work that most practitioners (even the gods, sometimes) do not completely understand the underlying reasons things work. Magic is ever likely to remain a somewhat empirical sort of science.
