Useless at exploration? It’s something more you can ignore (8,5)
I believe the answer is:
optional extra
'it's something more you can ignore' is the definition.
(extra which can be ignored)
'useless at exploration?' is the wordplay.
'useless' indicates an anagram.
'at'+'exploration'='atexploration'
'atexploration' with letters rearranged gives 'OPTIONAL EXTRA'.
(Other definitions for optional extra that I've seen before include "Non-standard feature" , "Selectable add-on" , "Non-obligatory addition" , "Non-essential additional item" , "Non-obligatory item" .)