Personal information on social media can be used for identity theft or social engineering.
What you post publicly can be used directly against you. Your mother's maiden name, first pet, childhood school, and birthplace are all common answers to account security questions — and they are often visible on your Facebook profile. An attacker who reads your timeline can reset your accounts without ever guessing a password.
Attackers build profiles. Your job on LinkedIn, your location on Instagram, your routine in Twitter posts, and your holiday photos on Facebook collectively reveal your home address, your schedule, your relationships, and your security question answers. This reconnaissance costs nothing and takes minutes.
Holiday posts announcing you are away from home — "Currently at the airport!" — are a documented enabler of burglary. Children's names and ages posted publicly make families targets for manipulation and grooming. The real-world consequences of online oversharing extend well beyond account security.
The practical defense: treat security questions as passwords. Give false answers that only you know and store them in your password manager. Lock your social media profiles to connections only. Do not announce travel until after you return. Be deliberate about what is permanently public.