Does this mean if we need to put the link to a specific CSS we can put it there?
You should open new threads instead, as it helps later users of the Community. (Threads can only be tagged Correct by the OP.)
The answer is: it depends. Custom Head HTML is not a frequently visited/visible area, so it's easy to lose track of special stuff you put in there. I would concentrate on adding to templates for consistency, to HTML blocks for visibility/manageability, and Custom HEAD only as a last resort.