In today's hyper-aware, security-sensitive age, the default attitude to Facebook is to double-down on privacy and keep content as well locked up as possible. Yet there are reasons why you should make some of your Facebook posts public for everyone to see—yes, even those people who aren't even friends with you (yet).
1. To help people find you
If there's a long-lost cousin or a new acquaintance desperately trying to find you on Facebook, then having your whole profile locked down isn't going to be very helpful—especially if you don't have a particularly indicative profile picture. A few public posts can help visitors distinguish you from all the other John Smiths out there. If you're worried about people finding you that you'd rather stay hidden from, just don't accept their friend requests, right?
2. To attract potential employers
By now you've probably all got used to the idea that a future boss might well look you up on Facebook before an interview. What is your potential employer going to find there? A blank page that says absolutely nothing about you (except you're a little secretive)? By making some of your best (and most professional) photos and status updates public you can provide a more rounded picture of who you are and what you're about to anyone who happens to find your Timeline.
3. To promote your work
If you have wares to sell, whether they're photographs or hand-made crafts, don't keep your promotions to your circle of friends—widen it out so the world at large knows what you've got to offer. Not only will your updates and links appear in more places on Facebook, they'll also get picked up by Google, Bing and the other search engines as well. Anything that gets more clicks towards goods made by you (or one of your friends) has to help in the long run.
4. To reach a bigger audience
Along the same lines as our last point, but from a less business-oriented perspective—all of your memes, jokes, and rallying cries can attract more shares and comments if you make them public. You're letting anyone chip in on the discussion sure, but that's not always a bad thing. Would you save your best one-liner for a private Twitter account? You never know, you might connect with like-minded people all over the world...
5. To use your Timeline as a landing page
Whether it's about.me, a Twitter profile, or a dedicated site, plenty of us like to have some kind of homepage on the Web that we can point people towards in an email signature or on a business card. As Facebook lets you select only certain posts and parts of your profile to make public, you can create a very effective landing page for yourself (complete with a few links to your achievements and an eye-catching photo or two) that has its own dedicated URL as well.
You'll find the audience selector setting below the status update box on the Web, in Facebook's mobile apps and most other places where you can post to your Timeline. The setting is remembered for future posts though, so just remember to change it back before you post something stupid that's for friends only.