No overload of work: Many messages should be transmitted only through the formal media of communication. As such the informal communication is not suitable to cope with the message load.
Overlooking superiors: Communication through informal channel leads to overlooking the superiors,
Interpretation changes: In a grapevine the key person passes the message to each person in a particular group. The members of this group in turn relay the message to some one else in another group. The process continues. This results in wrong interpretations, change of meaning, ideas and half truths.