Shivram Gangadhariah has sent a lucid write up on why we should insist on written messages when it comes to official and important communication and just not depend on the vagaries of sound waves.
At a crucial stage in Mahabharata, when asked for confirmation of the news, Dharmaraya announced to Guru Dronacharya "Yes, Ashwatthama, the elephant, is dead". Lord Krishna blew his conch in the middle of the announcement, ensuring that Drona only heard "Ashwatthama is dead". Heartbroken by the news of the death of his beloved son, the hitherto rampant Drona withdrew from the battlefield of Kurukshetra, thus changing its course. Now, if Dronacharya had insisted on a written statement instead of verbal communication, there would have been no scope for manipulation and confusion. Of course, it is not feasible to insist on written communication in mid-battle, but the above story shows the inherent risk in verbal communication.
It is quite possible that you work late hours to meet the client’s deadline and successfully complete module 13, only to find the client unhappily informing you the next day that he actually wanted module 30 done ASAP, not 13. Needless to say, the communication was all verbal, with no documentation whatsoever. It is pointless to argue with the client that “yesterday you had said 13, now you want 30 – how come?”, because client is always right (as is the boss, and the wife!). A short follow-up mail from you to the client immediately after receiving the verbal instruction, stating that “working on module 13, as per your instruction – please confirm” would have done the trick. It would have elicited a response from the client saying “OK, go ahead” or “Correction! I want module 30, not 13”. That would have resulted in a job well-done, and put smiles on all the faces that matter.
In intra-office affairs also, written communication helps avoid unnecessary headache. The strange notion that seems to be floating around of late, that mature people depend on verbal instead of written communication is … well, strange. Written communication does ease your work, but take care not to overdo it, like it is often done in Government offices. One of my previous employers, in the pre-email era, had intra-office memo with the catchy legend printed at top: “Don’t say - Write”. It did help reduce confusion, and the resulting friction.