Kathy Kleidermacher, author of Copywriter's Words & Phrases
– In my career I've not only written copy but also edited it. (...) So I can tell you from the point of view of your client or boss what I really appreciate – not having to clean up after you.– You want your writing to be smooth. Grammatical errors are like rocks in the road.
– Having a grasp of grammar will allow you to explain much more easily why you wrote something the way you did. And understanding the why behind the rules can also help you determine when you can break the rules without damaging the effectiveness of your writing. The real purpose of grammar is to make your writing clear to prevent miscommunication and confusion. That's why grammar rules exist. They're not there to limit your writing but to enhance it.
Lynne Truss, author of Eats, Shoots & Leaves
– Punctuation has been defined in many ways. (...) [One] writer tells us that punctuation marks are the traffic signals of language: they tell us to slow down, notice this, take a detour, and stop. (...) But best of all, I think, is the simple advice given by the style book of a national newspaper: that punctuation is "a courtesy designed to help readers to understand a story without stumbling".Isn't the analogy with good manners perfect? Truly good manners are invisible; they ease the way for others, without drawing attention to themselves. It is no accident that the word "punctilious" ("attention to formality or etiquette") comes from the same root word as "punctuation".
From The Right Word at the Right Time
Why bother with the right word? "People understand me well enough" is the typical response of the uncaring speaker to any criticism of his usage – that is, of the way he talks or writes. Butdo people understand such a speaker well enough? And even if they do, what is their impression of him or anyone who speaks and writes in a sloppy, careless way? Much the same, probably, as their impression of someone who is sloppily dressed. Using the right word at the right time is rather like wearing appropriate clothing for the occasion: it is a courtesy to others, and a favour to yourself – a matter of presenting yourself well in the eyes of the world.
Also see "The importance of good writing for professionals on all career paths", a collection of short articles that make some very good points – like this one by a certain Stephen H:
"People have expectations of professionals which includes that they have credibility. Nothing undermines that credibility more than simple mistakes. You can imagine a client thinking, 'Well, if they can't write a letter without errors, what chance that their advice is bad.'"
It is as well to embrace the truth that despite a lot of sloppiness and carelessness out there, good, correct writing is still highly prized in professional circles. Ignoring this fact could cost you; appreciating it could bring you great rewards.