There are no disadvantages to not having a LinkedIn profile. Many people don't. LinkedIn has a specific purpose, it's to create a professional network for yourself and to connect you to people in your industry or people with your interests.
There aren't any risks to not having a linkedin profile. Many humans do not. Linkedin has a specific cause, it is to create a professional community for your self and to connect you to people for your enterprise or people along with your pursuits.