Many companies have decided to bin their website and go for a customised Facebook page to maintain an online presence. Why it is easier to see why they would do this, a billion plus Facebook users are just waiting to like their site, there are some significant drawbacks to putting all your digital eggs in the Facebook basket.
One of the first things that springs to mind is the way that users interact with web pages and Facebook. Web pages are essentially a one way communication media, you put something on your page(s) and the user then goes along and reads it. It is not unusual to have websites where the content has not changed in a long time. This is not a bad thing for everyone, contact details and phone numbers will rarely change and can be left in a dusty corner of the web until someone asks for them but a lack of fresh content can very quickly lower your search ranking and put people off your site.