"The medium is the message," Marshall McLuhan wrote in 1964.
Marketing departments understand this to mean that the media used affects the *power* of the message. This power is measured by such things as "reach," "impact," "click-through," and "virality." In other words, marketing people measure *how many* people see the message and from there, how many of them take action based upon that message. This is, obviously, why advertising during major TV events is more expensive - it is also why large companies seem to always be running after the most popular online space to "have a presence." More eyeballs = more possible action.
What McLuhan meant, however, is that the medium affects the meaning of the message - in effect, every medium changes the message and affects the society in which that medium plays a role.
Your choice of medium affects your message.
This seems simple on the surface. But think about companies that try to communicate the same message across several media platforms. How effective is that same message portrayed in the same way in several media? It's a rare campaign that can manage this.
So how does this apply to your business?
It means that for every Great Idea TM you come up with, there is likely to be only one or two really good media on which to execute that idea.
Let's start with a simple idea - a store is having a Holiday Sale. They develop a 30-second TV commercial and buy media space on a Holiday special on TV in primetime. It's straightforward, simple. Now here's the Great Idea TM - someone thinks, "well, we already have a 30-second video...why not put it on a site like Youtube, where people can see it?"
Except, the medium changes the message. On TV, you have a captive audience. If they want to watch this show - unless they actively opt out by muting the sound or changing the channel, they will see your commercial. Online, you have to entice them to want to watch that commercial. Of course, you could buy ad time on a online show of some kind, and still have the captive audience (who has fewer options to opt out) but if you put your commercial on your website, or on a video sharing site, that ad better be darn interesting or people won't bother watching. In fact, the message needs to be completely different. There needs to be some entertainment value intrinsic to the video or you run the risk of viewers parodying it to add entertainment value for themselves.
You might have great label copy on your product - whimsical, slightly offbeat. If your Twitter writer keeps that tone, without understanding that sometimes a question has to be answered, not parried cleverly, the message is going to disappear in the "look at us, we're so cool."
Every time you come up with a Great Idea TM, consider the media that that idea is truly suited for. Don't try to multipurpose what isn't meant to be multipurposed. A website contest might work really well for people already inclined to visit your website, but could fail horribly as an ad reaching a broad, not necessarily interested audience.
Choose your medium, choose your weapon; from branding to sales to contests. Target the medium to the message and the message to the audience. Or risk the message being changed the moment it leaves your mouth.