There really is a benefit to using 60 card vs 40. Not only do get 2 more chances to stay alive, but have a wider area to build a deck that is more consistent. Meaning you get what you want, when you need it.
Thing is, you often have 20 Pokes and at least 15-16 Energy, but have very little room for the good supporters, trainers, or Stadiums if you should play them.
Listen to the experts here, 40 card decks are good way to get started, but when going deeper in, using the max 60 card deck.