カタカナは、英語のためにあります。 Katakata is for English.

salam hiragana its for the words originally Japanese and the katakana its for foreigner words so for example ali in Japanese its アリ but if you write it with hiragana it will be あり=ant=نملة here when he(ali) write his name in katakana they know(Japanese ppl)its an outside name not a Japanese one you can do the same things with (facebook youtube ...ect)

use hiragana for the words has Japanese origin and katakana for the Arabic names or foreigner things like facebook if we use hiragana with the all the words some word foreigners words if we write it in hiragana will have a meaning in Japanese like ali you want to say my name is ali they understand your name is ant(نملة)