Thinking about Katakana

I thought about Katakana since 2nihon asked me on the Twitter why Katakana is used for non foreign words.

Japanese character "Katakana" is often used for loanwords.
But it may also be used for regular Japanese words.
For example, ネコ(cat), ビン(bottle), メガネ(glasses), タンス(chest of drawers), イス(chair), or etc...
Of course Japanese people write these words using Kanji or Hiragana too.

I didn't know why they can be written by Katakana instead of Kanji or Hiragana.
(Or I'd not thought about that.)
If the Kanji is complex, it would be written by Hiragana or Katakana.
But why it could be written by Katakana instead of Hiragana?

In wikipedia,

Katakana are also used for emphasis, especially on signs, advertisements, and hoardings (i.e., billboards). For example, it is common to see ココ koko ("here"), ゴミ gomi ("trash") or メガネ megane ("glasses"), and words to be emphasized in a sentence are also sometimes written in katakana, mirroring the European usage of italics.

I think this is probably true.
But I don't think the emphasis is for the theme of the sentence.
I think it would be for people to be able to distinguish easily from other Hiragana in the same sentence.
Foreign people may not be able to distinguish Hiragana and Katakana.
But Japanese people can easily to do that.

Here is two sentences. Which is easy to read?

1. "私はめがねを買いに行きます。"
2. "私はメガネを買いに行きます。"

(In English, "I'll go to buy a pair of glasses.")
In 1, Hiragana-Hiragana-Hiragana
In 2, Hiragana-Katakana-Hiragana
2 is more easy to read, I think.
However, this is only my opinion.

And I also guess that Katakana is easier to write than Hiragana, because Katakana is formed from straight lines. :-)

For foreign people who is learning Japanese, you should not think about that.
Because many Japanese can read the word even if it would be written by Kanji or Hiragana instead of Katakana. ;-)
You'll be able to understand that if you would get experienced!