Robbery plot with no disadvantages (6)
I believe the answer is:
piracy
'robbery' is the definition.
(piracy is a kind of robbery)
'plot with no disadvantages' is the wordplay.
'plot' becomes 'conspiracy' (conspiracy is a kind of plot).
'with no' suggests deleting specific letters.
'disadvantages' becomes 'cons' (as in pros and cons).
'conspiracy' with 'cons' taken away is 'PIRACY'.
(Other definitions for piracy that I've seen before include "Robbery at sea or of copyright" , "Crime" , "theft" , "Maritime or commercial robbery" , "Act of plagiarism" .)