As txspots said, the back cinch should be tight enough to prevent a hind hoof getting caught in it. Sometimes a rider will start out with the back cinch pulled snug to the belly (but not tight), and then after the horse has been working a while, their belly draws up and the cinch gets too loose. (It would be a good thing at that point to tighten it again.) I have been involved in a wreck caused by a horse getting her foot through the back cinch - not one I was riding, but I was in the arena on my horse when it happened - and the mare totally destroyed the saddle, hurt the rider, and had soft-tissue damage to her leg. It really is a safety issue, not a cosmetic choice.
With the blanket leg straps, I adjust them to where they cross far enough below where the "cheeks" meet so that they won't chafe as the horse moves around, and I cross one leg strap through the other. I've never had a horse catch a foot in one, although I did have a mare back up to a fence post to scratch her butt on and catch the leg strap on the post. I have no idea how she did it, but I had to cut the leg strap to get her loose! Thankfully, she just stood there without fighting when she realized she couldn't go anywhere, and I don't think she was there for that long from looking where she was standing. I swear, horses will find a way to get hurt or stuck in a padded stall!
Hope this helps.