Why we need Expert power in project management?

PMP /Expert power in project management will enhance confidence in :---Project management and planning standards and procedures. Budgeting and cost control .Tendering management .Project capacity planning

Expert Power is means ability to influence some one with skills like technical abilities, Experience.It is needed for a project manager so that he or she can be a guide when required. Usually expert power comes with influence on technical abilities. I feel I can be a type of PM with referent power. Because a PM cannot have technical skills in all domain but can clearly manage different skills. What really important is inter personal skills and ability to build loyalty and trust. People usually don't work for companies but for the bosses.The major compliment as PM I have ever got was from a person who was released from my account and who had worked under different supervisor and when he said he still feels that I was the best of the managers he has worked with :)! I am lucky to have several compliments on similar lines.