When I bought my first box of 4x5 film, I didn't think twice about buying a box of twenty-five sheets as opposed to ten. The box of twenty-five wasn't particularly more expensive.
The thing is, when you're loading the film, especially when you're just getting used to it, it's easier to make mistakes. Back in the day, when I was shooting with my first view camera, I was using quickloads. Those don't exist anymore. Now, I'm using traditional film holders.
Of course, that means that I have to do all loading and unloading in complete darkness.
The thing is, if I make one wrong move, like I did the first time that I was loading my film holders, it's pretty easy to have your film slide out of place.
I have three film holders, which means that I can have six shots loaded at any given time. It's a lot easier to account for four loose sheets of film in that dark than it is to account for nineteen.