Aaron Marino of alpha m. is talking about why he never publishes videos regarding workouts for the neck, traps, and forearms. He doesn't specifically train them because they get a lot of work from doing everything else!
Whenever you grip, your forearms are working. Forearms get worked with any workout that has gripping. If you specifically training them, carpal tunnel can develop.
Certain sports need strong necks. Your neck gets enough work during the course of the day and workout. Why do you want a big neck anyway? Besides, Alpha has heard too many injury horror stories with guys just trying to strengthen their neck.
Your traps get enough work with back and shoulder exercises such as in pulling, rowing, pull ups, and side raises. They are engaged with these exercises. Traps can cause headaches from specifically working them. You can definitely injure yourself if working super heavy.