If one is walking the beach for snook less than 40 feet of line & leader is the norm. Sometimes it's like nymph fishing when there's about a rods length of flyline + leader and all you do is flick the wrist to get the fly in the water. Wading the mangroves about 40 to 50 feet is plenty of distance to hit the pockets in the branches, as I've probably spooked more fish wading right up on them on the flats when they should have been under the mangroves, because of old eyesight. If you're fishing out of a hull slap happy boat, then you'll need that 70 foot cast to work the mangroves so as to not spook the fish getting the boat too close.