My recommendation to churches is to always have a Facebook page that you use for advertising purposes. It's your message to the masses. This page is for promoting events and advertising service times. In addition to that, churches can also have one group page or multiple pages. You may want to have a group page for your youth group, prayer requests, or for your small groups to stay in contact. The pages can be more specific and more private.
My recommendation for small businesses is the same. The point of joining Facebook is to promote your business. As a small business, you could actually scare people off if you make them request to be added into a group. The only time you should have a group page is if you have customers or clients that you want to give them their own space maybe for communication purposes. For example, it is common for fitness centers to have a Facebook group for members only that is used for important announcements.
Remember that on Facebook, you can set your settings to restrict comments on your page and other privacy considerations. Manage your page well and you could help to reach people with your message.