WordPress will cache photos fetched from Flickr for up to 12 hours, so this means you my have to wait a while for any new photos before they appear on your WordPress blog.
Normally it is okay just to wait until the cache expires and your photos will show up.
However, if you were covering a live event and were updating the blog, adding photos and tweeting during the event you might want your photos to be updated on your WordPress site as soon as they were available.
You can do this using the parameter cache=”off”.
This causes Slickr Flickr to clear the cache every time a page is accessed and hence WordPress will go Flickr every time to get the latest photos.
Just remember to remove this parameter once the event is over and you have stopped adding new content.