I have seen MAXDOP work best when added as a hint within specific parallel queries after it being tested. 

However, I have seen that most programmers recommend it in the interest of reducing deadlocks.  MAXDOP does not stop or alleviate deadlocks especially in a hybrid environment. 

I have fought programmers on this suggestion and have proven my point.  Setting it at the server level may increase the performance of paralell queries (a handful) but however adversely affects all other processing.

Thanks.