Pointers mostly unnecessary (7)
I believe the answer is:
needles
'pointers' is the definition.
(needle is a kind of pointer)
'mostly unnecessary' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'unnecessary' becomes 'needless' (similar in meaning).
'needless' with its final letter taken off is 'NEEDLES'.
(Other definitions for needles that I've seen before include "Conifer leaves" , "Rocks off Isle of Wight" , "Isle of Wight feature - irritates" , "Isle of Wight chalk monoliths" , "Pointers - goads" .)