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_?




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.




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.

