What are the rules for katakana usage?

Are there any rules at all or is it at everyone's own discretion? Long story short, there was a list of groceries that anyone could add to for an upcoming group camping trip. I saw ソーセージ, ネギ, and 辛ラーメン. I thought I'll add ダイコン. I come back a bit later and someone had crossed it out and written だいこん.

Was someone just being punctilious or was it something that had to be corrected?

by Oi-oi-oi-boi