If you have more than a handful of contacts on Flickr, you'll have a hard time keeping up with all the new photos uploaded to their streams. It's probably not the end of the world if you miss a few photos here and there, but it's nice to have the ability to keep up with certain people of interest.
I recently started subscribing to the RSS feeds of a small group of close friends and other people whose photos I don't want to miss. It's really great not having to remember to visit every single person's Flickr stream each and every day. Now, I just let the photos drop into my feed reader and I can quickly decide if I want to see it larger or leave a comment on the Flickr page.
You can subscribe to people's Flickr feeds at the bottom of their photo stream — you should see something similar to the image above. You can also subscribe to the group pools or specific sets from your contacts.