People often use PDFs to archive the current state of a webpage (and can then use apps such as Skim to mark it up with highlighting, etc.). The feature is almost perfect at this point with its existing capabilities, but inserts page breaks. Sometimes, people want PDFs not for print purposes but simply for archival -- and allowing the omission of page breaks would be a big boon for such purpose. See also "Export PDF" feature in Saft plug-in for Safari.