Nothing put together can be practical (2,3)
I believe the answer is:
of use
'be practical' is the definition.
(useful)
'nothing put together' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'put together' becomes 'fuse' (fuse can mean to join).
'o'+'fuse'='OF USE'
'can' is the link.
(Other definitions for of use that I've seen before include "Having a function" , "Handy" , "Nifty" , "Advantageous" , "practical" .)