Had a job interview at a major European airline two days ago, I was asked quite a few things from ATPL subjects and they wanted to see my ATPL results and sittings. So yes, quite a big chunk of it, from an operational/practical point of view it is very important to know. They are never going to ask how the inner mechanism of a tachometer works, but do expect questions ranging from PoF to Performance, from Ops to Meteorology.
The QBs are only necessary to pass the EASA exams, which at the moment they are pure rubbish.