Because you first need to test for it. Well, since you can not perform this task if the users current profile is not loaded to look at, you would use RUNONCE which runs AFTER the users profile is loaded. Then you should be able to check and alter as needed without running the script over and over and over again, which is what it would do if you just had it in the RUN section of the Registry.

HTH... Please post again if you need a better explanation or further assistance.