Audience, or perhaps "readers" is a better term for text/discourse, defines many communication situations. That is, who you are talking to or writing to is often the most important aspect of a document or speech. The problems for writers are at least twofold: helping them understand this component of a communication, and helping them figure out how to adjust what they plan to say to that audience.
Audience is really part of a larger concept called a "rhetorical situation." Lloyd Bitzer coined this term to refer to the way that language (that is, rhetoric) can be used in situations in order to move towards a solution to the problem under discussion. When we write or speak in a situation we always do so for an audience (and almost always an audience external to ourselves). For this reason, we need to understand that audience so that we may adjust our discourse to them. These adjustments of language are the "rhetoric" of the situation.
In my most recent podcast, "Audience and rhetorical situations," I talk about how audienceis a key component of rhetorical situations; exigence (the perhaps best thought of as the problem or issue under discussion) is another key component, along with constraints (the range of possible solutions). These components are important both for academic writing--the exigence for my podcast--but also for workplace writing. For LinkedIn readers, workplace exigencies abound: what demographics should we focus our advertising on? Which project is most important to our unit? Where are we in our progress on our strategic plans?
Even more importantly, workplace communication tends to target audiences in much more specific and obvious ways than academic communication. For this reason, when you write or communicate at work you need to have an even more sophisticated understanding of why your are writing (the exigence), who you are writing for (are you writing to someone more or less powerful), and what the possibilities are for solving a problem through language (the constraints).
So what should you have remembered or taken from the writing courses that you took as a post-secondary student? What counts as good writing is highly context specific. That is, good writing in school contexts is not what counts as good writing in workplace contexts. More specifically, many workplace contexts differ from one another in what they value as good communication. Your job is to have a good theoretical understanding of communication--exigence, audience, constraints--and apply that understanding to the workplace you find yourself in.
For more information about this and other podcasts, visit wecanwrite.ca, follow me on Twitter (@rogergraves), or visit the Writing Across the Curriculum page at the University of Alberta.