I've been fortunate enough in my career as a lawyer to observe a wide variety of lawyering styles, and receive input from people at many parts of the spectrum.  One person whose input was not particularly palatable at first, but whose input ultimately turned out to be among the most valuable I call "the formatting czar".  This person was literally a formatting extremist.  He nitpicked documents as much as the next person, but what really set him off were "formatting issues".  He would spend hours on a pleading making sure the line numbers matched up to the text . . . perfectly.  I mean hours.  Over time, he expected you to pick up on these formatting rules - which seemed like quirks at the time - and he had little patience for nonconformists.  (And to date, I haven't had personal experience with any other practicioner whose formatting matches up.  If you want to see good formatting take a look at a US Supreme Court opinion, or a Supreme Court brief filed by a well respected lawyer.  I'm not sure whether they do the formatting themselves, but the formatting care put into these documents is readily apparent.)

In reviewing a document which someone else recently drafted, I noticed a few "formatting issues," and I compiled a rudimentary formatting checklist:

1. consistent use of smart quotes vs. straight quotes
2. inconsistent use of emphasis
3. font (and font size) discrepancies within the document
4. inconsistent use of defined terms
5. use of punctuation next to a quotation
6. use of semicolons vs. colons within the same list
7. formatting of sections (e.g., variations in tabbing, or some sections which have descriptions and others which do not)
8. underlining the period in a section title
   
9. switching between the section symbol and the word "section"
10. spacing in citations
    

The list is endless.  If you have a wordprocessing or proofreading department you probably do not need to worry too much about these things. (I'm not sure how common this is these days . . . .)  If you use Microsoft Word then you have to constantly battle the formatting spirits which seem to inhabit this program.  Struggling with Microsoft Word formatting demons is not fun.

But above all, something to keep in mind is that consistency is key.  Nothing conveys the fact that you have drafted the document in a hurry or without paying full attention more easily than inconsistent formatting.
 
[NB:  the above list is rudimentary at best and does not touch on things like font selection and typesetting.  Assuming you get past first level formatting issues, it's well worth spending time reading something like the Seventh Circuit's typography guide.  Also, lest it is not obvious, I do not adhere to the formatting rules closely on the blog, and in practice I'll readily admit I'm not perfect.  But it does not hurt to aspire to formatting perfection.]