One example where value arrays could be handy.

You could do the following inside the loop or outside and either way it would work as expected:

     byte[256] buffer = default;

     for (int i = 0; i < buffer.Length; i++) 
           buffer[i] = ... ; 

     byte* ptrNeeded = &buffer[0];
     . . .

One example where value arrays could be handy.

Did you mean pinned arrays? If not, what's a value array?

Oh, I see, your syntax byte[buffSize] buffer = .... Presumably a stack-based array that doesn't behave like stackalloc.

Yes. That would be just a struct with a length and indexer. (like Go arrays)
Length would have to be a constant expr though, which is not a problem here.

You could use pinned array also.
That would make the finally unnecessary, but then you would need to get the pointer and KeepAlive the array until done. Not sure if that is worth the trouble for this case.

Not sure if that is worth the trouble for this case.

Yeah i considered doing that and decided it wasn't :)