You use ready made sentences and expressions for a usually superficial conversation, so you do not need to use your inteligence or reveal any emotions. You can also use common knowledge or a distanced scientific approach to talk about things in an uninvolved way. At the same time you can pretend you care or are involved, when in fact the conversation and the topic are completely indifferent to you.
When is it used?
Some people use it always. It's such a handy thing, allowing conversations to happen without any real exposure. It is the best way not to come close or get to know anyone and not to be known as well.
Giving an unsolicited lecture to an acquaintant.
Small talk about the weather or "How are you? Well, thanks, fine."
Saying one had the emotions the listener would expect you to have, e.g. "When my daughter was born it was the most amazing thing in my life!" instead of talking about the real thing.
Using a lot of local expressions and easy jokes, e.g. "I hate you"; "estou noutra onda"; "é a vida"/ "such is life"...