The most common and most likely answer to this crossword clue is the 7 letter word EXERTED
I've seen this crossword clue in The Guardian
E
X
E
R
T
E
D
Buddy explains!
The straight part
We know that "Made effective use of" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case made effective use of = exerted.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EXERTED mean?
EXERTED verb- To put in vigorous action.
- To make use of, to apply, especially of something non-material.