While a dble haul may be used as a crutch to compensate for poor casting simply put no matter how you cast, adding a double haul adds distance. For some, 50' is sufficent for others not. While it generally works for me in fresh water, in the salt, with the wind and desire to be able to cast better 50' casts doesn't cut it.

My generalization is that there is no standard. Being able to cast in the situation you find yourself is what you need.
Yesterday I fished and did not need to cast more than 20', I was nymphing. Next week I'll be in the boundary waters and every inch of casting will come in handy.

jed