Since I have only a basic dual-lnb setup I don't speak from experience, but here's my understanding.

A multiswitch keeps each lnb half permanently set to a single polarity (i.e. odd or even transponders) by sending it a constant 14 or 18 volt signal. Thus ALL transponders are available at the switch at all times. The switch just flips each receiver to the appropriate odd-or-even lnb half as needed.

When you get into more complicated setups caused by viewing multiple satellites, etc., the switching requirements as to which lnb you connect each receiver to get more complex, but the basics of keeping each lnb (or dual lnb half) permanently set to a single polarity remains true.