Poor grammar and spelling that cause a requirements model to be inaccurate, or difficult to understand and use, are serious because they negatively affect the documentation’s ability to serve its purpose. An otherwise solid, easy to understand document with some errors in grammar and spelling, is not as serious. In either case, poor grammar and spelling should be included in the offending analyst’s professional development plan, and improvement should be encouraged and expected.
A friend of mine once told me of an uncle whose “byline” – for lack of a better term – was, “your name is safe in my house.” What he meant is that you wouldn’t have to worry about him or others in his company speaking ill of you. People took the uncle at his word, too, because he was never heard speaking poorly of others.