Felix Delbruck writes:

>But is it not conceivable that there will be cases where the exposition
>repeat continues to be used as a convention, but with no clear
>ramifications for the musical substance?

If you conclude such, then you are you not implying that composer was
in some sense in error, either out of negligence or stupidity? If you
can conclude this about a repeat sign, why can't you conclude this about
other aspects of the work's structure, or harmonic progression, or rhythm,
or ...

>what justifies the repeat (other than the fact that Schubert wrote it!)?

What other justification is necessary? Once we feel free to second
guess the composer's justification for any aesthetic decision, how do we
decide how much second guessing is legitimate and how much intrudes on the
composer's prerogative as the composer? Again, I believe that where the
composer wishes the interpretor to exercise judgment, the composer gives
clear indication thereof (e.g., ad lib, ossia, ...)

len.