*coughs* A snorkel is primarily for keeping dirt out of the filter when driving in a line on clay or fine sand. *coughs* It does help in water crossings too but if you dunk 20% of the car in water it's a risky move, at 50% it's can be dangerous. Especially if you are not in a convoy.
Get one if you like the looks. If you need one start planning another route around the obstacles. Save the use for when you are out of options.
I'm sorry, but that makes no sense and is flat out wrong. A factory air box and proper filter would do a much better job than a snorkel. The entire purpose of a snorkel is for fording water without risking your engine. I think what you're getting at is that most people who install snorkels don't water proof the rest of the vehicle. Raising breather lines, ensuring bearing and shaft seals are in good order, waterproofing connecters, running positive pressure in diffs/t-case/transmission, lifting any control modules above the water line, and much more should be done to really water proof your vehicle.
And obviously it's better to take the safest line. But a snorkel is another tool that enhances what lines you can take, just like 4wd, a lift, good tires, etc.