Aprendendo inglês com programas de TV

I don't know if that one question that I'm about to make is related to the "Inglês Falado" topic, but someone once told me that if you are trying to learn english based on watching things (basically anything that can be shown on television) you should be aware of sitcoms (situation comedies) as in this type of programs it is used another kinda of "language", I just didn't get it right, if it's because they may use a lot of slangs (that may be one of the reasons) or if it's because ofthe way people speak doesn't actually follow the grammar structure in the most part of the time.

Does anyone knows if that happens? Could you please give me an example of how the sentence's structure may change and the correct form of it following the grammar rules?

Thanks a lot.