Facebook has made the subscribe setting an opt-in feature instead of defaulted to on. The Subscribe button is designed to allow people to subscribe to your public posts rather than (or possibly in addition to) requesting a friendship.  You don’t approve subscribers. All of your current friends are, by default, subscribed to your posts.

Whenever you update your personal profile, you can determine who you want to see your post: public, friends or custom. Custom can then include friends of friends, only certain friends, or a friends list. You may want to check out this post to help you create friends lists and also review other privacy controls: 4 Simple Steps to Control Your Facebook Privacy.

If you want to keep your profile private, you don’t have to worry about the Subscribe button at all. But if you’re interested in sharing some posts publicly, you can opt in by going to www.facebook.com/about/subscribe and clicking Allow Subscribers. You can also read more about how the Subscribe button works at that link.

Once you click Allow Subscribers, you have some settings to configure. You can always go back and adjust these settings by clicking your profile in the upper-right corner of Facebook and then selecting Subscribers on the left sidebar. Then select the Edit Settings button in the upper-right corner of the page.

Decide if you want to allow comments by anyone on your public updates. Realize that you cannot block profanity or spam on your personal updates (even though you can on a Facebook page). You can always delete comments and block people after the fact, but if you keep this setting open, watch your posts.

When you allow subscribers, make sure you are watching how you post your updates. The default is public; so if you don’t want your post to be public, use the dropdown menu to change who can see the post. You can also retroactively change who can see your posts by using the dropdown menu to the right of each post. This is handy if you “over-shared” something private.

You may just choose to subscribe to people who have too many friends and aren’t accepting friend requests. If you navigate to their profile, you will see the Subscribe button, which indicates that you can choose to request a friendship or subscribe (or both).

But realize that if you do subscribe to them, your name is listed as a subscriber for public information. This is different than the “Likers” of a Facebook page, which are not visible to the public.

Source: Social Media Examiner