[ChrisH]

Originally Posted by dlavery

For any of a number of very legitimate reasons there may be various periods during a project where the expertise, knowledge, insight or skills of one particular person are so critical that they are irreplaceable.
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Or maybe they are just the only person with the key to the work area and they get stuck unexpectedly someplace other than where they are needed.

I really enjoyed Dave's comment about the inverse too. I have been involved with such people more times than I care to remember. Nice to know I'm not the only one.