You know exactly what you are putting into your body. When you make something from scratch you have complete control over ingredients. You can alter things to your dietary needs, and season/flavor to your liking. More often than not making something from scratch is going to provide healthier food than buying boxed. The cake I made is only a little over 100 calories per slice because of a key substitution...BLACK BEANS instead of oil. Yes, you read right, black beans lol. You can't taste them at all, and the cake is perfectly moist, without the addition of oil.
Pride. There is a greater sense of pride when making something from scratch. Because you take the time and measure out all the ingredients it feels like more of an accomplishment.
Time. Hands down, making something from scratch will always be more time consuming than making something from a box. This is the number con.
Dishes. You will most likely end up using more pots, bowls, blenders, mixers, etc. when cooking from scratch, especially when baking.
Here is my cake side by side with the photo of the cake from the recipe lol. I promise you I am MUCH better at piping icing than this looks, but I was using a ziploc bag with an end cut off, and not an actually piping bag lol