As XYZ says you need to know it to pass the exams, however a lot of the syllabus is very relevant to your day to day flying as an airline pilot.
The difference of course is that many aspects of a very broad range of subjects become much more specific to the type of operation you are engaged in. Additionally a lot of computerisation is tooled in to make the subjects more more user friendly.
However it is good to have ( or at some point had ) an in depth understanding of the various ATPL subjects and performance. Even though the subjects become more focused in the real world, a broader understanding is often part of knowing where to look for information when problems arise.