If you post often, you will see an immediate spike in News Feed impressions, but it’s generally not worth the cost in lost fans. When your fans see two status updates from you in their News Feeds, they’ll likely get annoyed, and will consequently unsubscribe or un-fan. There are few exceptions to this rule.
If you post too infrequently, you’re missing out on opportunities to reach your fans. Over the course of a year, a page with 10,000 fans that posts only half as often as they could misses more than 1 million chances to get their content in front of a hyper-targeted Facebook audience. The larger your fan page, the more often you should be posting — without annoying your fans.