This encrypts your msn conversations from being snooped on which is very useful when your sending sensitive data such as passwords and talking about blackhat stuff, both people in chat must have this for the channel to be encrypted, i use it all the time and its a great tool.
Nice share Xinapse, but I'm moving on to Skype now, I never really have liked MSN as it's where a lot of problems seem to start, however once configured and A-patched, it can run well.