Of course that is important, but there is also risk that, if this 不可替代的事情 is something technical... you'll get stuck on your current position....
I've seen cases that one guy have performed so well in a certain role that people think he'd better stay at his current position...
I think broaden your skills across various functions of the organization is important as well.... Specialized is good to quickly move to middle level, but too specialized is a bottleneck to move further.
