What does "Don't work too hard." mean?

Is it a good thing to say that to someone you care about and if they have been working and busy? Or would that be bad?
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+1 y
Also, say if somebody says this: "Well, don't overwork yourself." Would it be best to put a smile ( :) ) at the end or just leave as is - which one would show more care.
What does "Don't work too hard." mean?
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