I only use the foil because I got suck back on two straight beers. One when lagering and one with just a cold crash. And while star san in beer is no biggie...I'll pass. I do smaller batches so I have less thermal mass and probably drop the temp quicker than 5 gallons or bigger. I bet the larger the batch size the less likely it is for suck back.
Crashing helps to clear the beer of "some" of the yeast and other bi-products still in suspension. Drops the heavier particulates to the bottom. It also compacts the yeast cake and makes it a little easier to rack off.
I find that I get considerably less sediment in my bottles than those beers that I don't crash.
I just crashed my most recent two batches outside. Our recent cold spell had us at about 32 overnight and 50 during the day. I bottled them yesterday after sitting on my patio for 3-4 days.