In the classic no-knead bread recipe, it calls for letting the dough rise once for 12-18 hours, then folding it on a work surface and letting it rise again for two hours. Why is this second rise necessary? Could I just let the bread rise once for 14-20 hours with the same effect?
The second rising is quite necessary for good, light, airy bread.
When you fold the bread and then shape it into a proper loaf, you compress it, pushing out some of the air pockets that grew when it was rising. If you don't let it rise a second time after shaping, the bread won't have the proper airy-ness and it will be very dense.
You can't shape the bread properly at the beginning, so you must do it in two steps.
I suppose that if you're OK with dense bread, you can fold and shape it and then put it right in the oven but I don't think you'll like the outcome.