Principled negotiation works well because it is outwardly focused. Standard positional bargaining, on the other hand, focuses entirely on self. The first establishes common bonds and a shared search for solutions. The latter produces isolation and engenders ultimatums. Either may result in agreement, but the first builds relationships for the future while the second often leads to resentment and distrust.
Principled negotiation is especially crucial when an imbalance of power exists between the parties.
Hone your negotiation skills through education and practice. Do your homework. Use the Internet and other sources to learn all you can about the issue in question, research your options, and understand marketplace conditions. Your power in a negotiation will increase proportionately to the viability of your alternatives. Establish a team relationship with the other party as rapidly as possible to engender cooperation and set the stage for principled negotiation.