Well not entirely true it will cost you something in your labor ,but Flickr is a great way to catalogue your products or services. Not only does it thumbnail your pics but it also allows viewers a chance to see high resolution pics as well. For a cragislist, yelp, flipped or other social media site that allows you to post stuff for sale you can embed a link to view these images. Craigslist for example allows you to post photos but there resolution is not that great.

For an artist, studio, or designer Flickr is a must to gather a following and a great way to exposure of what you can do.

For a retailer its a great way to have a catalogue of your products that you can easily point to and if your hard drive crashes or you lose an image a great place to easily store them as well. Just remember it is out in public for all to see, use or grab.