2) Written communication is important for almost every job:
Effective communication is crucial in business and is listed amongst the essential requirements in most job descriptions. If your spelling and grammar are poor, your ability to communicate is hampered. Most of us will spend a decent chunk of our working day writing – whether that’s sending emails, preparing proposals or writing reports. Since the job you’re applying for likely involves writing it’s understandable that an employer will favour a candidate with superior writing skills. After all, wouldn’t you?
On top of this, an employer has to consider the impression your writing skills will give of them. If (for example) you’re emailing clients and customers, your mistakes will in turn reflect badly on your employer and their brand.