Is it generally best practice to have a single Document Center for a company, with various Document libraries for different areas of the company, or create multiple Document Centers, perhaps by department?
Both of them can be deployed in this case , but before that ,you should compare and consider which scenario is suit for you .
Multiple Document Center :
Advantages : Let each department manage and store their own files and policies , much safety .
Disadvantage :It very hard to manage for an Administrator .
Single Document Center :
Only 1 site to store all files and items , much easy to manage .
For End users , they also prefer going to 1 place to find all your company policies , It is like one-stop-shop!
Disadvantage : If your organization are very huge , different department have own policy and be treated as departmental confidential , it is not very safety .