I don’t see other justifications listed in the book, but as I suggested, every table can alter the game's rules any way they like with whichever justifications they can come up with. Make the game your own. You don't have to do things exactly as the rules, the book, or the designers, say.
But I also suggest that before changing rules, it's a good idea to justify it. As in why you want to give players more options ands slightly higher power. Some reasons could be too few players to cover the necessary bases or that the adventure is slightly overtuned for your group.