A number of the sky boxes do not like momentary disconnection of the dish from the input, this seems to throw them into confusion, and normally requires a power down before they will receive Sky channels again. Amstrad and Pace are the worst affected.
This is what stopped these small switches from being used when Astra 2 was first launched. A lot of customers still had a dish capable of receiving German TV left on their walls and this was thought an ideal solution to retain some foreign TV, mainly after Sky Subscriber Centres claimed that there would be no disadvantages of moving from Analogue to Digital (the usual 'read from a card' automaton approach)
Later firmware in digiboxes has the added advantage of erasing any personal 'other channel list' set into the box when switching rapidly between one dish and another.