In short, a dramaturg does the homework for a production: historical context, social significance, unknown references, etc. By providing research, a dramaturg gives everyone working on the production the same foundation which directly enhances the performances of the actors, provides a resource for the creative team, and betters everyone's relationship with the text.
Essentially a dramaturg's role is to make everyone's life a little bit easier. By shouldering the research and work beneficial in mounting an accurate and focused production, a dramaturg most of all guards the integrity of the material.
