A comma can alter the meaning of a sentence substantially. For example, I noticed the following in the Age recently:
… a married woman Kieran had been her partner since Helensvale High (article by Michael Gleeson about 100m hurdler Sally Pearson in The Age, 5 Sept 2011)
Presumably Sally Pearson’s partner wasn’t a married woman rather oddly named Kieran – the author meant that Sally Pearson is now married to Kieran, who has been her partner since school; a comma after ‘woman’ would have made this clear.
Similarly, in a response to a grant application review, a colleague of mine wrote:
…regression techniques that cater explicitly for missing data such as Generalised Estimating Equations …
without a comma after ‘data’, the implication is that GEE are missing data instead of a regression technique that caters for missing data.