Minecraft wiki entry for Hunger_management, associated text: Disadvantages:
Cake requires several different items to craft: sugar, wheat, an egg and three milk buckets. Not only is a crafting table is required for the recipe, but the milk buckets are non-stackable.
Once cake is placed, it cannot be retrieved. If the block below the cake is broken, the cake will disappear.
Cakes need to be placed to be eaten, which means they cannot be eaten in places where one cannot build.
If you only eat part of a cake, you'll have to come back to that exact spot to eat the rest of it later on.
Is not stackable in Java Edition.
Restores just 0.4 saturation per piece, or 2.8 as a whole.