Can't I just use Facebook as my website?
The short answer is that you can, but just relying on one social platform for your entire online presence is not only less effective than developing your own website, but can be rather short-sighted. We definitely recommend having social media as a part of your marketing strategy, but keep in mind that Facebook especially has many limitations that could affect the way your business is presented to potential customers.
A stand-alone website will not have limitations on which devices can access it, whether or not users need to log in to see it, or whether or not the "Facebook gods" decide to suspend or even take down your page. Facebook is an ad-driven marketplace and over half of what is displayed to users is typically ads or ad-related content. There are many other platforms out there that may be better suited to your business needs and audience, though these will often be used in conjunction with a Facebook page.
Relying too much on one platform can potentially end in disaster. There is no guarantee that Facebook will still be around in ten years or that a better alternative won't come along and people will switch. Your financial advisor will tell you to "diversify your portfolio" and, similarly, the best marketing advice would be to "diversify" your marketing efforts for many of the same reasons.
A website also gives you much more freedom to display your brand and your company without the focus being on the Facebook brand. At the end of the day, Facebook is really marketing itself, not you, unless of course you want to pay them to.