I can't recall any times where this would have been useful to me or think of a situation where it'd be a deal breaker. I could contrive a bunch of other operations that are inefficient on file systems like this (remove every other byte from the file, why not?), but doesn't mean that literally any idea we can think up should be supported by the file system apis.
From Unix and Windows we are used that we can insert and delete the end of a file and that we can read, write and seek anywhere in the file, but a filesystem could potentially do much more: Inserting/deleting at the beginning or inserting/deleting in the middle.
Deleting at the beginning of a file would be handy for queues or logs and inserting and deleting in the middle is a common operation for text editors.
There are even more questions you could ask:
- Why not have tabular files that allow indexed access?
- Do we need hierarchical directories or do we need directories at all?
- What about adding tags to files?
- Why having a filesystem at all?
> And I suspect the fact that you can simulate the operation yourself is a major reason why the feature doesn’t exist: Time and effort is better-spent adding features that applications couldn’t simulate on their own.