What is the purpose of a single input, single output, bidirectional shift register?

Question

_{(source: edu.au)}
This is the sort of bidirectional shift register, I'm talking about.

I understand why the normal right shift is useful, but when you shift it left, all you're really doing is sending the data input straight to the output. Is there a useful reason for shifting bits in this manner? EDIT- I'm trying to understand how the when shifting to the left, the value int left most register is outputted at the right most end. It makes no sense. Shouldn't the output be what the input is when shifting left?

Thanks!

Answer 1

a) if during left shift the output signal immediately followed the input, output changes were no longer synchronous. (And the circuit would just act as a "buffer".)
b) when you shift it left, all you're really doing is sending the data input straight to the output no:
it shifts the FFlops' data right to left, capturing Input data in the rightmost one (the one driving Output data, clocking Input data straight to the output ). All but the latest capture become observable again when you switch to shifting right and shift, only.