SMEs will sometimes tell you that the information is the only thing that matters; spell checking and copyediting are unnecessary frills.
Not that we had any doubts about this, but I recently stumbled across a study done at Clemson University that demonstrates that correct information is regarded as less authoritative if poorly written:
Steven Jong 
That goes double for books written by well-known authorities in their fields. I can’t get past grammatypos even if only on the first few pages. If misplaced modifiers, bad spelling, and random acts of carelessness litter an author-written introduction, the book gets shelved. I’m too nice a guy to ask for my money back.
Sad, because there are lots of books that I’m sure could teach me something, if only I could forgive the initial insult to my understanding clear communication.
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