Should Negotiators Defer Details Until Reaching Agreement on Principles?

Karrass rightly says "Agreement on details is made easier when an agreement in principle has been achieved.  When talks on details break down later, the opposing negotiators can maintain momentum by returning to the principles previously agreed to."  Often better for negotiators to ignore the details until they agree on basic principles.  Sometimes that works beautifully because details can be easily deduced from principles.  On the other hand, sometimes parties deadlock on opposing principles.  In these cases, negotiators might find they can actually agree on details even though they start from different principles.