You don’t have to cream the butter and sugar, which is a frequent downfall in from-scratch cakes (butter not soft enough or too soft).I'm no expert baker, but I don't think I've ever used a box cake mix. I'm intrigued though....all the cake mixes I've seen you have to add eggs, fat and water, so what exactly do you get in the box apart from flour, baking powder and flavourings?
Also, I think most box mixes use cake flour, so it saves from having to keep a specialty flour around (or making up a cheat version).
Having made both many times, I will say, regardless of the final results, box mixes come together much, much faster, and you don’t need the eggs to be room temp, you don’t need to weigh/measure things (minus water and oil), so it’s just faster, and not by a little bit (at least for me).