Often SPS/WSS admins want to "force" a subscription to a doucment library or list etc... for a particular user. Usually so they dont have to go and do it themselves.
This can be handy for site owners of say a team site who want all users to be notified when a new event gets added to the team event calendar.
Well ... Jan has created a web part that does this. Very handy.... and with source if you want to take a look at how it works.