A clear and well thought through brand channel plan helps join the dots.
All brands use different channels, mostly depending on their demographic or geographic profile. For example, a pure online company such as Vaperama will mostly look to dominate their web presence, with supporting offline channels too, although given that they operate globally means that expenditure for off-line would be vast and unlikely to provide the return that they would want, then there is a company like Summerhill + Co, who provide luxury designer furniture, again here, wasting effort in expensive advertising that is poorly positioned and not focusing on the right audience will simply be lost, Etisalat are a UAE telecom that operates across the Middle East, and often need to build rand reputation and as such will need to cover all channels. Therefore understanding what you are selling, who may want it and where they hang out is imperative, not only in saving money on marketing, but also building the right kind of audience activity.
There are also some newer and more imaginative channels too, or new merging technologies etc, and some companies are better focusing on these areas. Either way though, understanding the right channels and then making sure all your channels are cross fertilizing your brand is imperative, so your off line channels feed into your social media channels, and vis versa.