Another advantage is that making your own x from scratch is fun and satisfying. Mayonnaise, mustard, soda, barbecue sauce, gravlax, liver sausage — it's fun to see the things people buy ready-made, and know you have the knowledge and ability to do it yourself. Sometimes it's enough better to be worth the effort; sometimes, like catsup, you find that the store-bought is better — but you still have the fun of doing it and the satisfaction of knowing for sure.