Just thinking about magic when it comes to gaming and GMing.
Magic isn't science. For purposes of this discussion, let's say that science are a set of fixed laws of reality, and/or the study and discovery of those fixed laws.
Magic isn't that. Magic is a set of beliefs, fixed laws, mutable laws, random events, and unexplainable phenomena. Science is replicable and discoverable - science is finding out what works and doesn't work and investigating reality. Magic is about influencing what works and doesn't work, and changing reality (to a varying degree and for varying duration.) Wave your wand and brew the potion and cast the spell and she loves you/he's on fire/it's now made of wood not metal.
It's only mostly consistent. It's helpful for players and GMs alike if magic is relatively consistent. That is, when you cast Fireball you get a fireball. When you cast Major Healing, you heal people. That is, in general. But it's also helpful to a GM if it's got an element of chance to it, and vagueness about its limits and its reliability.
Sometimes you roll a critical failure and you don't get that. The fireball spell fizzles out or a hostile fire elemental is conjured up and burns your face. The healing spell tears up the wound something worse. You mis-speak a few words and your spell of Forlorn Encycstment actually frees all of the victims of that spell in a large radius.
This is great for a GM. If I rule that, say, a Created Servant can do X, Y, and Z, and that turns out to be a great idea - fine, they can do X, Y, and Z. If Y and Z turn out to be terrible ideas, I can simply rule the next one can't do that anymore. Why could the previous one? Must have been a miracle, a special confluence of good casting and mystical alignment, or a sign of the changing rules of magic. I'm not breaking anything by changing how a spell works or changing a ruling from one way to another. Who is to say that magic always works the same way? In worlds with active gods and mortals that can change reality with a handwave and a little bit of energy, why should reality always return to a homeostatic game-start norm? Or odd events suddenly determine what should be possible forever and always?
It's much harder with things that players and GMs alike expect to be scientific. If ST 18 means you can swing a two-handed axe one-handed, then it's weird if suddenly it can't do that anymore. If you can jump a 10' chasm with ease and then you can't, it's worrisome. If you can't assume your stats, skills, abilities mean the same thing this session as last session, it can be paralyzing. But if it's magic with built-in fuzzy edges of consistency, it's very changing nature is normal.
It's expansive. The vague limits of what magic can do means you can apply it anywhere. Whenever you need to pull in an element that could be enjoyable, you can pull it in with magic. Want dog-men? Magic some up. Need a cursed snake-headed woman who turns people to stone? Angry god with magic abilities magic'ed that one up.
As much as people hate, "A mad wizard did it!" most fantasy kind of falls down without that. Mad wizard made that ring in the Tolkein books. Mad wizard made the big dungeon that kicked off D&D's inception. Mad wizard did it is simply re-written as Angry god did it in in mythology. Mad wizard generally explains a lot. It's weak as the only explanation, but it's not generally a problem as part of the explanation in a game world dominated by magic.
As a GM, this is pretty freeing - you can put in almost anything, take it back out as necessary, and have built-in fuzziness of effect that neither cripples players nor gives them too much power and too many options.
As a GM, I love having this tool.