The answer is:
1. You don't need to if you are very knowledgable, and believe you can get
part of that buyer agent commision.
2. You need a good buyer agent if you are not very knowledgeable, and easy
to be bluffed.
From my experience most buyer are not very knowledgeable, and will be paying
actually higher price than having a buyer agent. A good buyer agent will
save you money much more than his/her commision.