Basically, they like it if your digibox calls back to confirm that it's still in use at your address. If you don't leave your digibox on standby (switch it off at the wall) then it can't make it's weekly (or monthly Ican't remember how often it checks) overnight callback to Sky (this is a free call that just lasts a few seconds). Basically this confirms that you haven't moved to another location while having your digibox registered at your current address. A lot of expats move to Spain or other European countries and take the boxes with them, while leaving it registered to a UK address (usually a relative) so that Sky can still pick up their bill. Receiving UK TV channels abroad via Sky is frowned upon and they try and take measures to stop it.