1. GD&T give clear concept of defining a part coordinate system on a part or assembly for making accurate and easy understanding through out the manufacturing process.
2. It will help you do the geometrical dimensioning, solve so many design problems
3. It will help you to reduce the drawing notes very drastically. Only one symbol can describe so many notes of the drawing. Complex drawing dimension can be understood without and complex notes with symbols of GD&T.
4. GD&T concept such as MMC, LMC Maximum material condition and minimum material condition can also simplify the drawing dimensions. It is saving the cost of gauging and manufacturing jigs.