You can use this under following situations:

• Download all images from a website
• Download all videos from a website
• Download all PDF files from a website

wget -r -A.pdf http://url-to-webpage-with-pdfs/

Grab all of a certain type of file listed on a web page and put them in the current dir. The example will use jpeg's.

wget -r -l1 --no-parent -A "*.jpg" http://www.website.com/pictures/