Blurring a license plate online can be accomplished for two reasons: protecting your privacy or preventing being incriminated. If the phone number falls into the wrong hands, it is possible to track down the owner's information. Whether or not you've done something wrong, it can also be reported to the police.
It's a matter of restricting your visibility to possible criminals, stalkers, and other troublemakers by blurring out your license plate. If that's something you're passionate about, go ahead and do it. It's fast and easy to do, and it'll make it more difficult for anyone to bother you.