E-Mail
The disadvantages of E-Mail rather than face to face communication are much the same as SMS:
It is difficult to understand sarcasm and what mood your recipient is in.
It’s impersonal and can make your recipient feel as if you can’t be bothered with them.
If your giving instruction or asking your recipient to perform a task they could read the message incorrectly or misinterpret it and you will not know this is the case as without facial expression or body language you cannot tell if someone is confused or at a loss.