This command gives you a realistic cake that you can actually eat. And every time you do, it loses durability. So when you place it on the ground, it's missing the slice that you ate.
And since each cake slice gives you back one full hunger bar, that means eating all seven slices will heal a total of seven hunger points, making it the best food source in the game, beating out steak and even rabbit stew. It's even better than the suspicious stew that gives you the saturation effect, which in total only gives you 6 and 1/2 hunger points. And since the command also makes cakes stacked to 64, there's no reason why you shouldn't make them your main food source from now on.
Well, besides how annoying they are to craft.
