If we create new Managed Property, we can't enable "refinable" as Yes – active, or Yes - latent.
So it is always better to use "empty" managed properties that are enabled as refiners by default, which come OOB.
By "empty" I mean that a crawled property is not mapped to it. This means that Site collection administrators can map a crawled property to one of these refiner-enabled managed properties.
Ref: http://blogs.technet.com/b/tothesharepoint/archive/2013/11/07/plan-to-use-refiners-on-a-search-results-page-in-sharepoint-2013.aspx
