Printing a webpage directly often wastes paper on ads, sidebars and navigation bars that have nothing to do with the article. A print friendly extension reformats the page into a cleaner layout first, and usually lets you remove specific images or paragraphs before you print or save it as a PDF.
Removing ads and clutter before printing
The main job of a print friendly extension is stripping out ads, navigation bars, comment sections and sidebars so only the article content remains. Better tools let you click to remove any remaining element you don't want, and preview the cleaned page before you commit to printing it.
Saving a webpage as a clean PDF
Most print friendly extensions can export the cleaned page as a PDF instead of printing on paper, which is useful for archiving articles or sharing them without the surrounding ads. Check whether the extension keeps links clickable in the exported PDF, since some flatten them into plain text.
Chrome's built-in print options
Chrome's own print dialog has a Background graphics toggle and a way to select a print destination like Save as PDF, but it still prints the page as designed, ads included. A print friendly extension goes further by editing the layout itself before you reach that dialog.