A question almost as old as humanity
In official letters, spelling is often the only correct thing; I actually prefer typos over grammatical errors.
From painful experience, I know that spelling mistakes in free texts spanning several pages are inevitable.
Yes, you write the text, you read it, leave it for a day, read it again... consider it error-free and print it out... wtf... still find another mistake... correct it and put it in an envelope... the junk comes back after the office circulation and you find some other careless mistake again...
If only I had paid better attention in German class, I was always deducted 2 grade points.