So you can save it as an .app file, which will run when you double-click it. Or you could save it as a Plug-in for Finder, iPhoto, etc ... and then you can right click an item in the Finder and choose Automator and then select the action. You can even save it for use with Folder Actions, so that it runs automatically when a folder's contents are changed.
Even though I'm still struggling with Automator (Is it just me, or is it still a bit hard to work out some of its quirks?) I've been able to find a lot of useful ways in which the workflows can be saved to run automatically.