A majority of searches today are of local intent. As opposed to your singular Facebook Page that has just one location, any search would lead to the relevant Facebook Page based on the location of the user.
You get more online citations by having separate Facebook Pages for each location of your business, aside from your flagship page. This will give you a larger presence on search engines and the Facebook Search.
You generate more reviews! Having separate pages would also help customers give reviews that are specific to the products/services of that particular location. You’re making it easier for your customers.
You can also tailor your content marketing strategies location-wise. Content that is relevant to one location might not be so for others.