I just came from a place in which the performance calculations were the bailywick of the flight engineer. All crewmembers were expected to maintain proficiency and to demonstrate regularly use of the performance calculating programs and documents. Wise crewmembers always took it to heart that while the flight engineer might be a consummate professional, he may also make a mistake. Accordingly, we always verified what was given us. I always do.
I find with my current, temporary position, performance training given at the company level has been lacking. As a check airman and company instructor, I have an opportunity to correct that, and have been working hard to do so. I firmly believe all crewmembers (flight deck crewmembers, that is) should be 100% proficient and understanding in their approach to performance calculations.
It's important stuff.