If you've got the right intelligence and happen to know a few people 'here n there' , a number plate/car rego can give someone as much info as they want. Especially crims looking for address's etc ... Can go deeper than that also to find out how many adults live at that address etc .. ie: For the purpose of breaking in to find keys.

Each to their own, but i would never post pics of my car anywhere with rego showing.