I will never understand why we have words that are pronounced the same but not spelled the same am people get upset over which way you spell it. If I can stand face to face with you an speak these words you only need the context to tell them apart. So why when I write them down do you suddenly need them to be different words to keep you from getting confused?
When speaking face to face, or even over a phone, you have other cues to the meaning- body language, inflection, facial expression, etc.
With written language the only cues are in the writing, so it is easier to misunderstand or miscommunicate. Therefore, clarity and precision are critical.
Right or wrong, sloppiness in written communication can imply a sloppy attitude or a lack of education. Your clothing and grooming can impact the way people perceive you. Written communication can convey a similar message and have a similar effect.
For many people bad spelling or bad syntax has an effect similar to fingernails on a blackboard.