Standards and Guidelines promote common practices to make systems more robust, have fewer errors and be more maintainable. Conventions and standards are meant to encourage the development of a common understanding of how a piece of software should be written and to set minimum expectations of the developers.
Standards are intended to facilitate the exchange of ideas and to assist developers in understanding others work. They are also intended to reduce the learning curve of developers who are new to a team.
No set of standards is ever complete or final. Rather standards evolve as techniques are refined and as new ideas are tested and adopted or discarded. No standard is sacred and cannot be improved upon or replaced at some point in the future. However, they do represent the concerted effort on the part of a development team to establish an understanding of how work is to be done and as such they must be either conformed to or changed by agreement of the team.