Folding works if you're very careful with your alignment, otherwise...zigzags. I hate that and I'm lazy so I'd rather rip and trim than fuss with trying to exactly line up folds for a truly straight cut. For me, it's faster and I'm less twitchy about frayed edges than I am about zigzags so that's what works for me!
I might not rip if it were something I intended as an heirloom quilt just because it MIGHT damage the fibers beyond my cuts (I don't know if it does or not)...but I consider all my quilts so far to be "useable" so that's not an issue for me. I want them used to death, loved and worn out so I have an excuse to make more! LOL