Why Are Passive Forms Used?

In passive, impassive sentences, the form different, like i said, you have to have the the b, auxiliary verb. In many cases, the agent is not included in the sentence at all. For example, this song was written by michael jackson. So essentially, though, it's a b auxiliary verb and then a past participle. Ok. Now, point two, why is the passive used? Well, er, it's sometimes thought that passives are not necessary. Er, some students that i meet say that they don't think native speakers even use them,. And that teachers teach them just because they have to. One thing i can say for sure is