I was always frustrated in English class as we learned the myriad rules to stylized writing. It occurred to me that while there are rules to writing correctly, those rules are somewhat flexible.
Writing organic SEO copy is flexible to the extent that you can write just about anything you want, however there are points to be gained for technical correctness.
With search algorithms becoming more and more sophisticated by the minute, it is becoming ever more important to include proper sentence structure and punctuation to set yourself apart from the masses. Proper punctuation, in particular, will not only help your readers get through your ideas, but will show the search engines that you are writing something more important that a love note to a high school crush.
And as you can imagine, Google and the other search engines are interested in understanding the difference between a silly note and a serious article.
Take care to include punctuation in your content. Punctuation will help you get your point across in a meaningful manner, and will appeal to the search engines as they digest your sentences and organize the keywords. Take care, too, to add highlighting. Highlighting is also recognized by the search engines, and when used properly can provide a little extra credit to specific keywords and phrases.
I have be reading an excellent book titled Eats Shoots and Leaves. This hilarious book is a great introduction to punctuation and proper use of language. Give it a try, and make sure to include punctuation in your organic content.