The main advantage why people eat junk food is that it's very cheap, so everyone can afford it. Another one is that it's usually quick to prepare, so you don't waste your time. But junk food has a lot of disadvantages, like: it's very unhealthy, and you don't know what's inside. Also, it increases the cholesterol and it has a high sugar level and you can get fat,that nothing want it.
On my opinion, you should never eat junk food because, although it's cheap, it's very unhealthy for you.