I figure locally on your streets you have no choice, it's the law. Police who are 'good' only use it on duty and you have minimal risk of personal invasion from those in your community.
The internet is a different beast. It reaches over 1 billion people, some who hate your lifestyle or could care less about your community. Who is to say there is no hack into registration databases or no unauthorized lookups. Plate obfuscation is just a small veil of deterenenc on your identy. However, there still are many more methods for those who are not deterred..