da vinchi and michaelangelo both worked from begining to the end all their career lives for others. almost all the art works of their proliferated were works of commissioned (which meant paid by others)
practice is a technical means lead to perfection of skills and those are not art works per se. (still, sketches...) just as would you call a prototype of your technical concept a product? of course not, it leads to a product. but that even already went too far compraing to still studies, nude studies
basically practice...
