Yeah, I think that's one of those things JKR has really failed to think through properly. The way she seems to have set it up, there's really no reason why people like Remus or the Weasleys can't just transfigure their shabby old stuff into shiny new stuff, or just change some rocks into whatever they need.
I could fanwank some of it away. Like, maybe wizard manufacturers put anti-transfiguration spells on the things they make and sell. They'd kind of have to, otherwise no one would ever buy new clothes or furniture or anything, and everyone would go out of business. And I've theorized, like you, that transfiguring an object into food actually burns up more calories than the food you end up with. But it still doesn't explain why Remus can't transfigure a pile of dirt into a nice set of robes for himself.
The only think I can come up with is that it's not permanent. Maybe Dudley's tail would've gone away on its own if the Dursleys had waited long enough. And maybe the duration of the effect is unpredictable, so if you go out in your nice transfigured robes, you might find yourself in the middle of Diagon Alley wearing nothing but a pile of dirt.
Of course, that raises the question of what, exactly, Transfiguration is good for. It's treated like an important subject at Hogwarts, but if you can only change things temporarily, then it's only of limited use outside of school.
no subject
I could fanwank some of it away. Like, maybe wizard manufacturers put anti-transfiguration spells on the things they make and sell. They'd kind of have to, otherwise no one would ever buy new clothes or furniture or anything, and everyone would go out of business. And I've theorized, like you, that transfiguring an object into food actually burns up more calories than the food you end up with. But it still doesn't explain why Remus can't transfigure a pile of dirt into a nice set of robes for himself.
The only think I can come up with is that it's not permanent. Maybe Dudley's tail would've gone away on its own if the Dursleys had waited long enough. And maybe the duration of the effect is unpredictable, so if you go out in your nice transfigured robes, you might find yourself in the middle of Diagon Alley wearing nothing but a pile of dirt.
Of course, that raises the question of what, exactly, Transfiguration is good for. It's treated like an important subject at Hogwarts, but if you can only change things temporarily, then it's only of limited use outside of school.