The right message and the right channel for delivery determine communication success.
What happens if I choose the wrong channel to communicate?
If you choose the wrong channels -- that is if the channels are not effective for the type of message and meaning you want to create -- you are likely to create misunderstanding, and even end up worse off then if you had kept the message to yourself. Not only does using the wrong channels impede communication, but doing so can cause mistrust in others, particularly about your sincerity and commitment to them.
Example: Let's say a departmental manager of 15 employees decides he wants to convey the message that he values their work and well-being. He has a number of ways and channels he can use to do this. He can walk around and talk face to face with his employees on a regular basis, wishing them good morning, and inquiring as to their welfare (that's one "channel"). He could send a memo out each morning wishing them good morning (that'd be another channel). Or he could send an email.
The question is "Which channel would be best for this message?" Walking around and talking face to face is the most "costly" in terms of time and managerial commitment, while the other two are not costly. But consider the reaction of employees. How many employees will get the meaning the manager is trying to send, if the channel is an automated email? Worse, how many employees will question the manager's commitment if he chooses an email channel to transmit a message that is clearly not suited to the channel?
That's just one example. The more emotionally loaded the message, the more thought has to go into HOW to communicate it, and which channels to use.