The reason this is important is because a one-size-fits-all solution may not be possible. For the case of physical rewards in return for pledges, charge-up-front is completely unnecessary. The creator can just say that the rewards will go out after they receive payment on the first of the month, so someone subscribing in the middle of the month receives nothing until the month ticks over. For the donation case, charge-up-front is useful, but not for the reason you might think. The main point is to prevent freeloaders who pledge, view the exclusive content, and then cancel without paying a cent. In this case, creators would probably be fine with pro-rating the first monthly payment after charge-up-front, or even just skipping it entirely. It's all donations anyway, so the point is not to extract maximum value from each patron, it's to make sure each patron is paying an amount that they are comfortable with, so that they will continue to pledge long-term.
My overall point is that the platform that is Patreon is abstract and flexible enough to support a number of different business models, which may have different needs with regard to charge-up-front and other features. And to get an idea of the full breadth of those possibilities, I think you just need to interview a lot of creators, and I think you'll find that the usage patterns are more varied than you expect. At the same time, I'm sure there's value for patrons in having things like charge-up-front work the same way across different creators' Patreon accounts, so that they know what to expect when pledging.
And as a patron, I appreciate receiving my December rewards near the end of December rather than mid-January.