Clients tend to assess the credibility and business expertise of photographers based on their attention to the details displayed in their written and oral communications, in addition to their people skills. Clients then relate to the photographer "on that level".
That is called making an impressiom. Making a poor impression ultimately costs a professional photographer money.
A client is less inclined to try and take advantage of a photographer who projects in their written and oral communications that they are sharp, literate, and professional. Photographers who demonstrate a sloppy attitude to communicating accurately always seem to have client horror stories and wonder why they have so many client problems.
Of course this is the day of the Internet and texting, but I sincerely doubt that anyone routinely using poor spelling and grammar on the Internet, subsequently demonstrates excellent literacy skills when dealing directly with people, clients or not.
In online forums, a posters credibility is also part and parcel to making an impression, and not using the appropriate capital letters in a post dims ones credibility considerably by making a poor impression.
Excellent spelling and grammar skills certainly will not hinder one's progress in any job, business or profession.
