The importance of not being at a loose end (4)
I believe the answer is:
note
'the importance' is the definition.
(I've seen this in another clue)
'not being at a loose end' is the wordplay.
'being at' is a charade indicator (letters next to each other).
'end' indicates one should take the final letters.
The final letter of 'loose' is 'e'.
'not'+'e'='NOTE'
'of' is the link.
(Other definitions for note that I've seen before include "mention" , "Annotation; tone" , "Eminence" , "Consequence" , "held by piano teacher" .)