What does "at an immediate disadvantage " mean?
Mr Morgan says those who can't spell are at an immediate disadvantage in the workplace.

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Answer

It means that they have a disadvantage as soon as they start working.
This is differenent from a disadvantage that might show itself slowly over time.
If a person started work without the ability to spell, it would show up in their work on the first day.
If a person was not good at tecnical expertise, this might take somewhat longer for his/her boss to notice.

Answer

exactly, we'll get loss-of-function