Old saddles falling apart: that's completely useless (4,4)
I believe the answer is:
dead loss
'completely useless' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'old saddles falling apart' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'falling apart' is an anagram indicator.
'o'+'saddles'='osaddles'
'osaddles' anagrammed gives 'DEAD LOSS'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for dead loss that I've seen before include "unprofitable" , "Unproductive person/thing" , "Unproductive person or thing" , "Useless person or thing - sounds moribund and profitless" , "write-off" .)