It lets someone gain some information about you, but it’s not inherently damaging by itself.
The address can give a general idea about your geographical location (city or region). This doesn’t pinpoint an exact address but can still provide a vague idea of where you are.
They can overwhelm your IP address with traffic in a DDoS attack, which can make your internet connection temporarily unusable.
They could scan open ports associated with your IP address to reveal what services are running on your device which could have known vulnerabilities.
If they have other means to monitor network traffic they could determine what websites you’re visiting or who you’re communicating with.
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