If u have ONLY ps3/ps4 account, the psn account works as additional authentication so importance of another security token is low. If u have also a pc service account, u need to be extremely carefull if u want to skip token. That means knowing how to protect urself agianst all popular hacking methods (like phishing, keyloggers, poorly protected 3rd party website hacking, dictionary attacks, brute force attacks etc). There is also something called session hijacking, but security token has no effect on it.