I am a dual citizen of Hong Kong and the Philippines, and I am traveling from Hong Kong to Japan. Japan does not require visas for Hong Kong passport holders, so I used my Hong Kong passport to buy a ticket. I am wondering if it could ever be harmful to bring my second passport with me. I plan to bring both passports just in case, as I do not see any harm in doing this.
I have found several articles that suggest bringing both passports, but I have also found one article that suggests only bringing one passport. My mother, who also has dual citizenship, is a flight attendant and has been told by her company that dual citizen flight attendants should leave their second passports when traveling. She accepted this without questioning it, and I asked her to ask the proper authorities about it, but she has no time. She originally insisted that I leave my second passport at home, but has since relented.
I would like to know if there is any reason why bringing my second passport could be harmful.