Well, it announces to the world that you're using WordPress &mdash and, worse, a specific version of WordPress. That presents a trivially identifiable signature for particular versions; and that, in turn, facilitates attacks against them. So why not just lie about it if you're so concerned? Your mother approves of this lie. We promise.
Note: If you want to be nice to the WordPress folks, leave "WordPress" in, but put in a nonsense version number (or none). If you want to entirely remove the meta tag, simply leave the content field blank. This is also not real security, but it can't hurt.
0. Install and activate plugin.
1. Set version value.