I can choose between:
End UserDeveloperConsultantCommunity ManagerExecutive
What is it for?
I do not know the exact reason for the classification, but I think it is really so people can understand your role in regards to Linux use and administration.
One of the goals of the site it to allow members to market themselves to potential employers, by choosing consultant, developer, etc... you can indicate to potential employers what professional level you hold. I personally will never list myself as a consultant because I will not consider working as a consultant.