Really poor — so save? (7)

I believe the answer is:

useless

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'really poor' is the definition.
'useless' can be an answer for 'poor' (I've seen this before). I am unsure of the 'really' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for useless that I've seen before include "Having no benefical function" , "Without purpose" , "Having no beneficial function" , "Lacking in purpose" , "Counterproductive" .)

I've seen this clue in The Independent.

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