So what is the case when adding conv=sync,noerror makes a difference when backing up an entire hard disk onto an image file? Is conv=sync,noerror a requirement when doing forensic stuff? If so, why is it the case with reference to linux fedora?

Edit:

OK, so if I do dd without conv=sync,noerror, and dd encounters read error when reading the block (let's size 100M), does dd just skip 100M block and reads the next block without writing something (dd conv=sync,noerror writes zeros to 100M of output - so what about this case?)?

And if is hash of original hard disk and output file different if done without conv=sync,noerror? Or is this only when read error occurred?