Why it matters
People decide whether they trust you partly on how you sound. If your website's chatty but your sales emails read like legal letters, customers notice. They might not be able to say what's wrong. It just feels a bit like dealing with two different companies.
Words are also one of the cheapest ways to stand out. Plenty of businesses in your sector probably look similar and sell similar things. Sounding like actual humans can set you apart without a big rebrand.
And it helps your team. Once everyone knows how the business should sound, writing gets quicker. There's less second-guessing, and far fewer emails that start with "Please be advised". (Eugh.)