...makes people think twice before applying patches that do not apply to thier problem. (You would be amazed at the number of people that will apply every patch they can get their hands on even if they don't need them.)
...opens up two way communication to allow MS to give you updated information on a hotfix and to allow you to report that the hotfix worked or if it caused any problems.
...provides realtime feedback on the number of people that really need a hotfix.
In other words it helps them gather the information they need both to decide how big the problem is and how to fix it.