Why are katakana preferred over hiragana or kanji sometimes?

I noticed that "dame", which means "not good" or "don't do that", is sometimes written in manga as katakana. I was wondering, is it because katakana is used to express a strong feeling?

Sometimes, there are also other words written in katakana. In general, what are possible reasons why people would choose katakana for a word instead of hiragana or kanji, especially when that word is not usually spelled with katakana?

Answer

In addition to user458s list:

• To give visual and/or very slight semantic emphasis. Almost like using bold or italics in English.

それはだめだよ！

それはダメだよ！

You can see that the latter stands out more. As for the onomatopoeia, those are often a little emphasized too, so it probably overlaps with reason 2 a good amount.

• Plant, animal, and mineral names are often written in katakana.