Theses and articles typically go through many versions, ding-dong to-and-fro between supervisors and co-authors. Some people keep track of the version number (or date-last-modified) by giving each draft a different file name. Personally, though, I tend to get inconsistent with the file naming, especially when it's 2:30am. So I figured it might work better for me if the date-last-modified was printed in the PDF of the thesis/article draft itself.
One could always put the date in the header or footer, but there might already be some content in those regions. Besides, it's probably not a good idea to mess with the formattings for a journal article. Instead, I put
\today in a watermark, so the date would get updated I compile my draft:\usepackage{draftwatermark}
\usepackage{datetime}
\ddmmyydate
\SetWatermarkLightness{.9}
\SetWatermarkText{Draft\string@\today}
\SetWatermarkScale{.6}
The colour, lightness, font and other attributes of the watermark are configurable. I also used the
datetime package to configure the date formatting. Here’s how the output looks like (a page from my thesis draft):
