Anyone can write, right?
Yes, anyone who isn’t illiterate can write, but not everyone is is literate writes well. Many people can cook too, but cooking abilities vary widely. Gordon Ramsay explains the differences in cooking ability using very colorful language on his TV shows.
Professional editing doesn’t come cheap, especially if the editor is highly experienced. However, the price is cheap relative to the consequences of bad writing.
Many life events are one-shot opportunities for your writing to make a difference, such as applying for a well-paying job or a prestigious graduate program. Other examples include submitting an academic manuscript to a top journal or submitting a business proposal for a large project. The reality is that most of these situations involve stiff competition. If your writing fails to impress, you lose that opportunity.
A clear and precise piece of writing without a single error signals two things: attention to detail and intelligence. The former is easy to understand, but the latter is not so obvious at first glance.
Clear and precise writing signals intelligence because your thoughts and ideas can transfer unambiguously to the reader. A poorly written piece is intellectually inaccessible because the poor writing obscures the brilliant ideas within. Compared to a poorly written piece of work with brilliant ideas, a well-written piece with relatively less brilliant ideas appears more outstanding simply because those ideas are accessible.
Professional editing is not cheap, but it is worth its weight in gold. An opportunity lost because of poor writing is an opportunity lost forever.