No: (a) it only works on elements whose parents are the full viewport width, such as the body (simplifying the rules a little—there’s much finer nuance to the

No: (a) it only works on elements whose parents are the full viewport width, such as the body (simplifying the rules a little—there’s much finer nuance to the interpretation of percentages), and most of the places you might want viewport units aren’t suitable; and (b) that’s literally just a longwinded way of writing “100%”, because mathematics.