Why are standards so important for members of the engineering design team?

The American National Standard Drafting Manual - Y14 provides the basic standards which are important because they provide a system for the entire team and allow the entire team to understand on how something can be designed.
Following rules or standards is a universally accepted method to gain any success on any level. Standards also provide a common method to communicate between the team and any other teams that might have to work on the design process.   

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