Let me tell you what I've meant.
Not all people do SEO to generate sales. Some people do SEO to get traffic to their sites to earn money from CPC ads, CPM ads or just to make the site popular. For this kinda person small spelling mistake will be okay.
But for people who target to generate sales, it can be a disadvantage sometimes,
Eg - you want to do SEO for the keyword "american pie" but mistakenly you write it as "american pee" > so mostly u won't make sales.
deer management = dear management
So, for sales, I think best way is not to make spelling mistakes when doing SEO. Sometimes a single letter can change the whole meaning of the sentence.
It's common sense. Even with correct keywords we pick the best keyword phrases over those which are useless.
I'm not talking about writing mistakenly. I was talking about taking advantage of typo keywords. When you do that you first make a page for correct word and then you make landing pages for this page using these typo words.
I have just realized that.
I agree with you 100% about avoiding spelling mistakes. The last thing I do when I finish a HTML page is running spell checker in Dreamweaver. This is one reason I love this tool.