I can appreciate a well-defined magic system, and I see the appeal; but I definitely lean toward "soft" in my own writing, at least so far as my couple of novel series are concerned. Never really sat down to think about why that's the case, but I guess now's my chance!
Pausing here to go look up the definitions of soft and hard systems, so that I'm sure I have half an idea what I'm talking about before I proceed to talk about it.
Okay, I had it more or less right. Let's go.
As for the question of "who cares", well, I think it matters. If magic is gonna feature heavily in your story, soft vs. hard is an important choice—although I don't see why you couldn't have both in a single work. I've seen many people express their love for hard magic systems, and as I said, I get it, the first Mistborn book was great fun because of it. The fact that it elevates engagement and enjoyment for many potential readers is reason enough, if that sort of thing matters to you as a writer.
Ultimately, for me, I think the choice comes down to what fits a particular story. I haven't really tried doing a fully hard magic system before, could be a fun future challenge.
I found a thing while googling, that describes hard magic as "being logically consistent, having clear rules and limitations" and soft as "having flexibility and a sense of wonder". Well, that pretty much explains why I tend to go soft—besides being a kinda lazy writer who likes to cut corners.
My two novel series are directly related to one another, so the magic is expressed in pretty much the same way, though bound by different soft pseudo-systems. The stories is meant to be quite absurd and surreal, and the magic is an extension of that; there's a distinct element of slapstick to spellcasting in my settings.
Some might consider it lazy writing, and I'm not even sure I disagree, but I'll try to make a case for how it's totally reasonable: To a significant degree, these stories revolve around larger-than-life forces having (or trying to have) their way with the world and the characters who live it. That's the Man vs. Nature, Man vs. Supernatural, and Man vs. Fate aspect of the stories, though in Eight Barrows Braves at least, those three conflict types are largely rolled into one and the same thing. Magic is a continuation of those forces, fleeting manifestations of them. Since these forces themselves are supposed to be poorly understood (by most) as well as highly mutable, the magic should echo that, and it doesn't make sense to tack a hard system onto it. I think the mystery, unpredictability, and sheer weirdness of the magic is suitable for this kind of story. I may have sometimes (ab)used it to plot my way out of a tight corner, but...
There is a certain order to it, but instead of making it explicit, I try to show throughout the telling what each type of magic, and each practitioner, is capable of. Maybe sometimes I'll pull strange rabbits out of stranger hats, in ways that don't necessarily constitute good storytelling.
There's another kind of soft magic I like to use, and that's the eldritch kind, the dangerous kind. I think magic in Cosmic Horror should always be soft, because a huge part of the appeal is the fear of the unknown. Nobody, not the reader, not the user, should know quite what their magic is capable of, how much it'll cost, and all the horrifying ways it could go wrong. That being said, I'm sure someone out there has proved me sorely wrong by creating an awesome hard magic system for the Cthulhu Mythos.
Yeah, I think it matters a lot, I think they're both great, and I'm Team Soft all the way, baby!
