For instance, it is really hard to refer to a diff you have in your IDE when instant messaging someone or filing a bug in an issue tracker
/ is a tool that combines project wiki, issue tracker and subversion GUI in a nice and usefual package. You can look at changesets as whole (something that subclipse doesnt offer), and you can refer from the wiki or commit comments to changesets and files via so-called trac links, which is an extended wiki syntax that would look like "r123", which generates a hyperlink to a diff representation of the complete changeset of revision 123. Very nice. And free.