Early draft yes. But when you write an early draft of prose or code, you leave yourself the ability to insert or remove material in a way that _changes the indexes of the tokens you already put in your draft_. If you write a letter, you may know that it ends with "Yours Truly, <your name>", but not know the absolute number of tokens the letter will use. In this framework, once you say that "Yours Truly, John Hancock" are tokens 501 to 506, infilling the preceding sentences requires that you exactly preserve the number of tokens before that point ... which to me seems silly. I'm sure it's computationally messy to be able to slide stuff around, but if it meaningfully changes the topology of the search process, it may be worth it.