3. You can impress your friends and neighbors with your skill and knowledge (or just be that weird person who makes yogurt).
4. More bacteria! Some commercial yogurt makers let their yogurt sit for a very short time, which prevents the helpful probiotic bacteria from growing. Then, to achieve the yogurty texture, they add strange and unnecessary thickening agents.
If the white yogurt you find in the supermarket has anything besides milk, (and possibly cream) and probiotics, such as acidophilus, that’s not true yogurt.