I guess it really depends on where you live. If you live in a area like mine (SE Michigan), you will absolutely not want to skimp on making sure nothing in your engine will freeze. I learned this lesson from my step dad that cracked the block on my uncle's boat.
I have a Volvo Penta 5.0 Gi. My first winterization procedure was:
1) Drain water hoses.
2) Remove drain plugs and remove debris from holes.
3) Remove thermostat so I don't have to wait for it to open and tighten housing back down. I guess the previous owner never reinstalled one because I don't have one. I will install one in spring along with a new impeller.
4) Reinstall drain plugs.
4) Reconnect all hoses with the exception of the water pump inlet hose.
5) Fill up the
Camco 65501 Do It Yourself Boat Winterizer with 5 gallons of -50 Marine/RV antifreeze.
6) Use the Camco Front Mounted Engine Pump Adapter (not needed for Mercs) to connect the Camco Winterizer hose to the waterpump inlet (the top one).

7) Turn the Camco valve on.
8.) Have assistant turn on engine.
9) As engine sucks in the anti-freeze, be sure to tilt the container back so the engine does not suck dry air.
10) Have assistant stop engine before the container is emptied.
11) Now time to do change the engine oil & filter, outdrive oil, gas filter, grease fittings, etc.
12) Have a drink, you earned it.